Hydrophilic and lipophilic balanced microemulsion formulations of free-form and/or conjugation-stabilized therapeutic agents such as insulin

ABSTRACT

A therapeutic formulation comprising a microemulsion of a therapeutic agent in free and/or conjugatively coupled form, wherein the microemulsion comprises a water-in-oil (w/o) microemulsion including a lipophilic phase and a hydrophilic phase, and has a hydrophilic and lipophilic balance (HLB) value between 3 and 7, wherein the therapeutic agent may for example be selected from the group consisting of insulin, calcitonin, ACTH, glucagon, somatostatin, somatotropin, somatomedin, parathyroid hormone, erythropoietin, hypothalamic releasing factors, prolactin, thyroid stimulating hormones, endorphins, enkephalins, vasopressin, non-naturally occurring opioids, superoxide dismutase, interferon, asparaginase, arginase, arginine deaminease, adenosine deaminase, ribonuclease, trypsin, chymotrypsin, papain, Ara-A (Arabinofuranosyladenine), Acylguanosine, Nordeoxyguanosine, Azidothymidine, Dideoxyadenosine, Dideoxycytidine, Dideoxyinosine Floxuridine, 6-Mercaptopurine, Doxorubicin, Daunorubicin, or I-darubicin, Erythromycin, Vancomycin, oleandomycin, Ampicillin; Quinidine and Heparin. In a particular aspect, the invention comprises an insulin composition suitable for parenteral as well as non-parenteral administration, preferably oral or parenteral administration, comprising insulin covalently coupled with a polymer including (i) a linear polyalkylene glycol moiety and (ii) a lipophilic moiety, wherein the insulin, the linear polyalkylene glycol moiety and the lipophilic moiety are conformationally arranged in relation to one another such that the insulin in the composition has an enhanced in vivo resistance to enzymatic degradation, relative to insulin alone. The microemulsion compositions of the invention are usefully employed in therapeutic as well as non-therapeutic, e.g., diagnostic, applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/509,422, filed Jul. 31, 1995 and issued Oct. 28, 1997 asU.S. Pat. No. 5,681,811; which is a continuation-in-part of U.S. patentapplication Ser. No. 08/276,890, filed Jul. 19, 1994 and issued Aug. 1,1995 as U.S. Pat. No. 5,438,040; which, in turn, is a division of U.S.patent application Ser. No. 08/059,701, filed May 10, 1993 and issuedOct. 25, 1994 as U.S. Pat. No. 5,359,030.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to microemulsion formulations of free-formand/or conjugation-stabilized therapeutic agents, and to methods ofmaking and using same. The compositions of the invention may comprisetherapeutic agents such as proteins, peptides, nucleosides, nucleotides,antiviral agents, antineoplastic agents, antibiotics, antiarrhythmics,anti-coagulants, etc., and prodrugs, precursors, derivatives, andintermediates thereof.

2. Description of the Related Art

In the field of pharmaceutical therapeutic intervention, and thetreatment of disease states and physiological conditions, a wide varietyof therapeutic agents have come into use, including various proteins,peptides, nucleosides, nucleotides, antiviral agents, antineoplasticagents, antibiotics, antiarrhythmics, anti-coagulants, etc., andprodrugs precursors, derivatives, and intermediates of the foregoing.

For example, the use of polypeptides and proteins for the systemictreatment of specific diseases is now well accepted in medical practice.The role that the peptides play in replacement therapy is so importantthat many research activities are being directed towards the synthesisof large quantities by recombinant DNA technology. Many of thesepolypeptides are endogenous molecules which are very potent and specificin eliciting their biological actions. Other non-(poly)peptidyltherapeutic agents are equally important and pharmaceuticallyefficacious.

A major factor limiting the usefulness of these therapeutic substancesfor their intended application is that they are easily metabolized byplasma proteases when given parenterally. The oral route ofadministration of these substances is even more problematic because inaddition to proteolysis in the stomach, the high acidity of the stomachdestroys them before they reach their intended target tissue. Forexample, polypeptides and protein fragments, produced by the action ofgastric and pancreatic enzymes, are cleaved by exo and endopeptidases inthe intestinal brush border membrane to yield di- and tripeptides, andeven if proteolysis by pancreatic enzymes is avoided, polypeptides aresubject to degradation by brush border peptidases. Any of thetherapeutic agent that survives passage through the stomach is furthersubjected to metabolism in the intestinal mucosa where a penetrationbarrier prevents entry into the cells.

In spite of these obstacles, there is substantial evidence in theliterature to suggest that nutritional and pharmaceutical therapeuticagents such as proteins are absorbed through the intestinal mucosa. Onthe other hand, nutritional and drug (poly)peptides are absorbed byspecific peptide transporters in the intestinal mucosa cells. Thesefindings indicate that properly formulated therapeutic agents such as(poly)peptides and proteins may be administered by the oral route, withretention of sufficient biological activity for their intended use. If,however, it were possible to modify these therapeutic agents so thattheir physiological activities were maintained totally, or at least to asignificant degree, and at the same time stabilize them againstproteolytic enzymes and enhance their penetration capability through theintestinal mucosa, then it would be possible to utilize them properlyfor their intended purpose. The product so obtained would offeradvantages in that more efficient absorption would result, with theconcomitant ability to use lower doses to elicit the optimum therapeuticeffect.

The problems associated with oral or parenteral administration oftherapeutic agents such as proteins are well known in the pharmaceuticalindustry, and various strategies are being used in attempts to solvethem. These strategies include incorporation of penetration enhancers,such as the salicylates, lipid-bile salt-mixed micelles, glycerides, andacylcarnitines, but these frequently are found to cause serious localtoxicity problems, such as local irritation and toxicity, completeabrasion of the epithelial layer and inflammation of tissue. Theseproblems arise because enhancers are usually co-administered with thetherapeutic agent and leakages from the dosage form often occur. Otherstrategies to improve oral delivery include mixing the therapeutic agentwith protease inhibitors, such as aprotinin, soybean trypsin inhibitor,and amastatin, in an attempt to limit degradation of the administeredtherapeutic agent. Unfortunately these protease inhibitors are notselective, and endogenous proteins are also inhibited. This effect isundesirable.

Enhanced penetration of therapeutic agents across mucosal membranes hasalso been pursued by modifying the physicochemical properties ofcandidate drugs. Results indicate that simply raising lipophilicity isnot sufficient to increase paracellular or transcellular transport.Indeed it has been suggested that cleaving peptide-water hydrogen bondsis the main energy barrier to overcome in obtaining diffusion of peptidetherapeutics across membranes (Conradi, R. A., Hilgers, A. R., Ho, N. F.H., and Burton, P. S., “The influence of peptide structure on transportacross Caco-2 cells”, Pharm. Res., 8 1453-1460, (1991)). Proteinstabilization has been described by several authors. Abuchowski andDavis (“Soluble polymers-Enzyme adducts”, In: Enzymes as Drugs, Eds.Holcenberg and Roberts, J. Wiley and Sons, New York, N.Y., (1981))disclosed various methods of derivatization of enzymes to provide watersoluble, non-immunogenic, in vivo stabilized products.

A great deal of work dealing with protein stabilization has beenpublished. Abuchowski and Davis disclose various ways of conjugatingenzymes with polymeric materials (Ibid.). More specifically, thesepolymers are dextrans, polyvinyl pyrrolidones, glycopeptides,polyethylene glycol and polyamino acids. The resulting conjugatedpolypeptides are reported to retain their biological activities andsolubility in water for parenteral applications. The same authors, inU.S. Pat. No. 4,179,337 (issued Dec. 18, 1979), disclose thatpolyethylene glycol rendered proteins soluble and non-immunogenic whencoupled to such proteins. These polymeric materials, however, did notcontain fragments suited for intestinal mucosa binding, nor did theycontain any moieties that would facilitate or enhance membranepenetration. While these conjugates were water-soluble, they were notintended for oral administration.

Meisner et al., U.S. Pat. No. 4,585,754 Apr. 29, 1986, teaches thatproteins may be stabilized by conjugating them with chondroitinsulfates. Products of this combination are usually polyanionic, veryhydrophilic, and lack cell penetration capability. They are usually notintended for oral administration.

Mill et al., U.S. Pat. No. 4,003,792 (issued Oct. 16, 1990) teaches thatcertain acidic polysaccharides, such as pectin, algesic acid, hyaluronicacid and carrageenan, can be coupled to proteins to produce both solubleand insoluble products. Such polysaccharides are polyanionic, derivedfrom food plants. They lack cell penetration capability and are usuallynot intended for oral administration.

In Pharmacological Research Communication 14, 11-120 (1982), Boccu etal. disclosed that polyethylene glycol could be linked to a protein suchas superoxide dismutase (“SOD”). The resulting conjugated product showedincreased stability against denaturation and enzymatic digestion. Thepolymers did not contain moieties that are necessary for membraneinteraction and thus suffer from the same problems as noted above inthat they are not suitable for oral administration.

Other techniques of stabilizing peptide and protein drugs in whichproteinaceous drug substances are conjugated with relatively lowmolecular weight compounds such as aminolethicin, fatty acids, vitaminB₁₂, and glycosides, are described in the following articles: R.Igarishi et al., “Proceed. Intern. Symp. Control. Rel. Bioact.Materials, 17, 366, (1990); T. Taniguchi et al. Ibid 19, 104, (1992); G.J. Russel-Jones, Ibid, 19, 102, (1992); M. Baudys et al., Ibid, 19, 210,(1992).

The modifying compounds are not polymers and accordingly do not containmoieties necessary to impart both the solubility and membrane affinitynecessary for bioavailability following oral as well as parenteraladministration. Many of these preparations lack oral bioavailability.

Another approach which has been taken to lengthen the in vivo durationof action of proteinaceous substances is the technique of encapsulation.M. Saffran et al., in Science, 223, 1081, (1986) teaches theencapsulation of proteinaceous drugs in an azopolymer film for oraladministration. The film is reported to survive digestion in the stomachbut is degraded by microflora in the large intestine, where theencapsulated protein is released. The technique utilizes a physicalmixture and does not facilitate the absorption of released proteinacross the membrane.

Ecanow, U.S. Pat. No. 4,963,367 (issued Oct. 16, 1990), teaches thatphysiologically active compounds, including proteins, can beencapsulated by a coacervative-derived film and the finished product canbe suitable for transmucosal administration. Other formulations of thesame invention may be administered by inhalation, oral, parenteral andtransdermal routes. These approaches do not provide intact stabilityagainst acidity and proteolytic enzymes of the gastrointestinal tract,the property as desired for oral delivery.

Another approach taken to stabilize protein drugs for oral as well asparenteral administration involves entrapment of the therapeutic agentin liposomes. A review of this technique is found in Y. W. Chien, “NewDrug Delivery Systems”, Marcel Dekker, New York, N.Y., 1992.Liposome-protein complexes are physical mixtures; their administrationgives erratic and unpredictable results. Undesirable accumulation of theprotein component in certain organs has been reported, in the use ofsuch liposome-protein complexes. In addition to these factors, there areadditional drawbacks associated with the use of liposomes, such as cost,difficult manufacturing processes requiring complex lypophilizationcycles, and solvent incompatibilities. Moreover, altered biodistributionand antigenicity issues have been raised as limiting factors in thedevelopment of clinically useful liposomal formulations.

The use of “proteinoids” has been described recently (Santiago, N.,Milstein, S. J., Rivera, T., Garcia, E., Chang., T. C., Baughman, R. A.,and Bucher, D., “Oral Immunization of Rats with Influenza Virus MProtein (M1) Microspheres”, Abstract #A 221, Proc. Int. Symp. Control.Rel. Bioac. Mater., 19, 116 (1992)). Oral delivery of several classes oftherapeutics has been reported using this system, which encapsulates thedrug of interest in a polymeric sheath composed of highly branched aminoacids. As is the case with liposomes, the drugs are not chemically boundto the proteinoid sphere, and leakage of drug out of the dosage formcomponents is possible.

A peptide which has been the focus of much synthesis work, and effortsto improve its administration and bioassimilation, is insulin.

The use of insulin as a treatment for diabetes dates back to 1922, whenBanting et al. (“Pancreatic Extracts in the Treatment of DiabetesMellitus,” Can. Med. Assoc. J., 12, 141-146 (1922)) showed that theactive extract from the pancreas had therapeutic effects in diabeticdogs. Treatment of a diabetic patient in that same year with pancreaticextracts resulted in a dramatic, life-saving clinical improvement. Acourse of daily injections of insulin is required for extended recovery.

The insulin molecule consists of two chains of amino acids linked bydisulfide bonds; the molecular weight of insulin is around 6,000. Theβ-cells of the pancreatic islets secrete a single chain precursor ofinsulin, known as proinsulin. Proteolysis of proinsulin results inremoval of four basic amino acids (numbers 31, 32, 64 and 65 in theproinsulin chain: Arg, Arg, Lys, Arg respectively) and the connecting(“C”) peptide. In the resulting two-chain insulin molecule, the A chainhas glycine at the amino terminus, and the B chain has phenylalanine atthe amino terminus.

Insulin may exist as a monomer, dimer or a hexamer formed from three ofthe dimers. The hexamer is coordinated with two Zn²⁺ atoms. Biologicalactivity resides in the monomer. Although until recently bovine andporcine insulin were used almost exclusively to treat diabetes inhumans, numerous variations in insulin between species are known.Porcine insulin is most similar to human insulin, from which it differsonly in having an alanine rather than threonine residue at the B-chainC-terminus. Despite these differences most mammalian insulin hascomparable specific activity. Until recently animal extracts providedall insulin used for treatment of the disease. The advent of recombinanttechnology allows commercial scale manufacture of human insulin (e.g.,Humulin™ insulin, commercially available from Eli Lilly and Company,Indianapolis, Ind.).

Although insulin has now been used for more than 70 years as a treatmentfor diabetes, few studies of its formulation stability appeared untiltwo recent publications (Brange, J., Langkjaer, L., Havelund, S., andVølund, A., “Chemical stability of insulin. I. Degradation duringstorage of pharmaceutical preparations,” Pharm. Res., 2, 715-726,(1992); and Brange, J. Havelund, S., and Hougaard, P., “Chemicalstability of insulin. 2. Formulation of higher molecular weighttransformation products during storage of pharmaceutical preparations,”Pharm. Res., 9, 727-734, (1992)). In these publications, the authorsexhaustively describe chemical stability of several insulin preparationsunder varied temperature and pH conditions. Earlier reports focusedalmost entirely on biological potency as a measure of insulinformulation stability. However the advent of several new and powerfulanalytical techniques—disc electrophoresis, size exclusionchromatography, and HPLC—allows a detailed examination of insulin'schemical stability profile. Early chemical studies on insulin stabilitywere difficult because the recrystallized insulin under examination wasfound to be no more than 80-90% pure. More recently monocomponent,high-purity insulin has become available. This monocomponent insulincontains impurities at levels undetectable by current analysistechniques.

Formulated insulin is prone to numerous types of degradation.Nonenzymatic deamidation occurs when a side-chain amide group from aglutaminyl or asparaginyl residue is hydrolyzed to a free carboxylicacid. There are six possible sites for such deainidation in insulin:Gln^(A5), Gin^(A15), Asn^(A18), Asn^(A21), Asn^(B3), and Gln^(B4).Published reports suggest that the three Asn residues are mostsusceptible to such reactions.

Brange et al. (ibid) reported that in acidic conditions insulin israpidly degraded by extensive deamidation at Asn^(A21). In contrast, inneutral formulations deamidation takes place at Asn^(B3) at a muchslower rate, independent of insulin concentration and species of originof the insulin. However, temperature and formulation type play animportant role in determining the rate of hydrolysis at B3. For example,hydrolysis at B3 is minimal if the insulin is crystalline as opposed toamorphous. Apparently the reduced flexibility (tertiary structure) inthe crystalline form slows the reaction rate. Stabilizing the tertiarystructure by incorporating phenol into neutral formulations results inreduced rates of deamidation.

In addition to hydrolytic degradation products in insulin formulations,high molecular weight transformation products are also formed. Brange etal. showed by size exclusion chromatography that the main productsformed on storage of insulin formulations between 4 and 45° C. arecovalent insulin dimers. In formulations containing protamine, covalentinsulin protamine products are also formed. The rate of formulation ofinsulin-dimer and insulin-protamine products is affected significantlyby temperature. For human or porcine insulin, (regular N1 preparation)time to formation of 1% high molecular weight products is decreased from154 months to 1.7 months at 37° C. compared to 4° C. For zinc suspensionpreparations of porcine insulin, the same transformation would require357 months at 4° C. but only 0.6 months at 37° C.

These types of degradation in insulin may be of great significance todiabetic subjects. Although the formation of high molecular weightproducts is generally slower than the formation of hydrolytic (chemical)degradation products described earlier, the implications may be moreserious. There is significant evidence that the incidence ofimmunological responses to insulin may result from the presence ofcovalent aggregates of insulin (Robbins, D. C. Cooper, S. M. Fineberg,S. E., and Mead, P. M., “Antibodies to covalent aggregates of insulin inblood of insulin-using diabetic patients”, Diabetes, 36, 838-841,(1987); Maislos, M., Mead, P. M., Gaynor, D. H., and Robbins, D. C.,“The source of the circulating aggregate of insulin in type I diabeticpatients is therapeutic insulin”, J. Clin. Invest., 77, 717-723. (1986);and Ratner R. E., Phillips, T. M., and Steiner, M., “Persistentcutaneous insulin allergy resulting from high molecular weight insulinaggregates”, Diabetes, 39, 728-733, (1990)). As many as 30% of diabeticsubjects receiving insulin show specific antibodies to covalent insulindimers. At a level as low as 2% it was reported that the presence ofcovalent insulin dimers generated a highly significant response inlymphocyte stimulation in allergic patients. Responses were notsignificant when dimer content was in the range 0.3-0.6%. As a result itis recommended that the level of covalent insulin dimers present informulation be kept below 1% to avoid clinical manifestations.

Several insulin formulations are commercially available; althoughstability has been improved to the extent that it is no longer necessaryto refrigerate all formulations, there remains a need for insulinformulations with enhanced stability. A modified insulin which is notprone to formation of high molecular weight products would be asubstantial advance in the pharmaceutical and medical arts, andmodifications providing this stability (and in addition providing thepossibility of oral availability of insulin) would make a significantcontribution to the management of diabetes.

In addition to the in vivo usage of therapeutic agents includingpolypeptides, proteins, nucleosides, and other biologically activemolecules, such agents also find substantial and increasing use indiagnostic reagent applications. In many such applications, these agentsare utilized in solution environments wherein they are susceptible tothermal and enzymic degradation. Examples of such diagnostic agentsinclude enzymes, peptide and protein hormones, antibodies,enzyme-protein conjugates used for immunoassay, antibody-haptenconjugates, viral proteins such as those used in a large number of assaymethodologies for the diagnosis or screening of diseases such as AIDS,hepatitis, and rubella, peptide and protein growth factors used forexample in tissue culture, enzymes used in clinical chemistry, andinsoluble enzymes such as those used in the food industry. As a furtherspecific example, alkaline phosphatase is widely utilized as a reagentin kits used for the colorimetric detection of antibody or antigen inbiological fluids. Although such enzyme is commercially available invarious forms, including free enzyme and antibody conjugates, itsstorage stability in solution often is limited. As a result, alkalinephosphatase conjugates are frequently freeze-dried, and additives suchas bovine serum albumin and Tween 20 are used to extend the stability ofthe enzyme preparations. Such approaches, while advantageous in someinstances to enhance the resistance to degradation of the therapeuticand/or diagnostic agents, have various shortcomings which limit theirgeneral applicability.

In general, the approaches of the prior art for formulatingproteinaceous therapeutic agents for enhanced stability in vivo do notprovide intact stability of such agents against acid and proteolyticenzymes of the gastrointestinal tract, the property desired for oraldelivery of protein drugs. In spite of this fact, intensive efforts arebeing made in pharmaceutical and scientific organizations toward oraladministration of protein drugs. These efforts have largely focused oninsulin as a protein drug of choice for developing oral dosage forms,but have not been successful in yielding formulations that replaceparenteral administration.

Formulations of free insulin using different techniques have beenattempted.

Liposome entrapped insulin for oral administration and its attendantdrawbacks have been described hereinabove.

A recent approach involves formulation of insulin in a liquid medium,using absorption enhancers. U.S. Pat. No. 5,653,987 (issued Aug. 5,1997) to Modi and Chandarana teaches that insulin can be formulated fororal or nasal delivery using at least two different absorptionenhancers. A close examination of the enhancers described in thisreference reveals that these enhancers are not pharmaceuticallyacceptable. In the examples provided in this patent, most contain eithersodium lauryl sulphate, a detergent known to damage the lining of thegastrointestinal tract, or polyoxyethylene 9-lauryl ether, which is usedin extracting protein from biological specimens, and additionally isknown to be spermatocidal in character. The formulation and synthesismethod of U.S. Pat. No. 5,653,987 (issued Aug. 5, 1997) differfundamentally from the concept and method of the present invention.Additionally, unlike the present invention, the formulation approach ofU.S. Pat. No. 5,653,987 (issued Aug. 5, 1997) does not addressenzymatically stabilized insulin conjugates.

Still another recent approach of free insulin formulation for oraldelivery utilizes the technique of microemulsion. This formulationapproach has been described by Cho, Y. W., et al, in U.S. Pat. Nos.5,656,289 (issued Aug. 12, 1997) and 5,665,700 (issued Sep. 9, 1997), byOwen, Albert J., in U.S. Pat. No. 5,646,109 (issued Jul. 8, 1997) and byDesai, Ashok J., in U.S. Pat. No. 5,206,219 (issued Apr. 27, 1993).

Cho, Y. W., et al teaches in U.S. Pat. No. 5,656,289 (issued Aug. 12,1997) that oral proteinaceous compositions comprising oil/wateremulsions can form chylomicra or provide chylomicra to sites ofabsorption in the gastrointestinal tract. Such patent teaches that thehydrophilic phase may contain ethanol. In the disclosed examples ofmicroemulsion preparations, a substantial amount of ethanol is needed inthe hydrophilic portion of the emulsion. Ethanol, however, is known todenature many proteinaceous drugs. Further, the method of manufacturingthe proteinaceous composition described by Cho et al. in U.S. Pat. No.5,656,289 (issued Aug. 12, 1997) involves microfluidization, which candamage or denature protein drugs as a result of the heat generation andshear force entailed in the microfluidization process.

In U.S. Pat. No. 5,665,700 (issued Sep. 9, 1997), Cho et al. teach thatproteinaceous compounds can be orally delivered in a water-in-oilformulation comprising a hydrophilic phase dispersed in a lipophilicphase to form an emulsion. Microfluidization with its aforementionedattendant drawbacks is also disclosed in U.S. Pat. No. 5,665,700 (issuedSep. 9, 1997) for preparing the microemulsion. Free insulin (insulinthat is not modified by conjugation with amphiphilic polymers, asdisclosed hereinafter and in U.S. Pat. No. 5,681,811 issued Oct. 28,1997, U.S. Pat. No. 5,438,040 issued Aug. 1, 1995 and U.S. Pat. No.5,259,030 issued Oct. 25, 1994, all in the name of Nnochiri NkemEkwuribe) is unstable in the gastrointestinal tract. In the examplesprovided in U.S. Pat. No. 5,665,700 (issued Sep. 9, 1997), mostpreparations disclosed by Cho et al. contain protease inhibitors.Inhibition in such formulations will, however, not be specific toinsulin, and inhibitors may cause severe gastrointestinal problems as aresult of inhibition of intestinal proteinaceous contents which areotherwise digestible. Further, lecithin complexation with insulin isrequired in Cho et al.'s microemulsion formulation. In the presentinvention, the use of lecithin is not essential.

As a result of the protease inhibition resulting from Cho et al.'sformulations containing protease inhibitors, indiscriminate absorptionof toxic proteinaceous material may result in the in vivo use of suchformulations. The formulations of the Cho et al. U.S. Pat. Nos.5,656,289 (issued Aug. 12, 1997) and 5,665,700 (issued Sep. 9, 1997) arebased on a concept and a method of manufacture that differ fundamentallyfrom the concept and method of the herein disclosed invention.

Another microemulsion formulation of free insulin is described in U.S.Pat. No. 5,646,109 (issued Jul. 8, 1997) to A. J. Owen. Owen teachesthat a water-in-oil (w/o) microemulsion readily converts to anoil-in-water (o/w) emulsion by the addition of aqueous fluid to the w/omicroemulsion. A close examination of the conditions necessary forconvertible microemulsion in the formulation of U.S. Pat. No. 5,646,109(issued Jul. 8, 1997) reveals that the resultant HLB (hydrophilic andlipophilic balance required is greater than 7. In one example describedat column 22, lines 26-28 of U.S. Pat. No. 5,646,109 (issued Jul. 8,1997), Owen demonstrates that his formulation containing resultant HLBof 4 produces a non-convertible microemulsion and has no effect inpromoting rectal delivery of calcitonin. The use of resultant HLB ofgreater than 7 to prepare a convertible microemulsion for oral deliveryof insulin is based on a concept that differs from the concept of hereindisclosed invention, as hereinafter more fully described.

Desai, A. J., U.S. Pat. No. 5,206,219 (issued Apr. 27, 1993) describesanother microemulsion formulation for oral administration, in which aliquid polyol solvent and lipid cosolvent containing a proteinaceousmedicament, e.g., insulin, is treated to form a microemulsion in thegastrointestinal tract at sites of absorption. Desai teaches that avital ingredient in the formulation is a protease inhibitor. The purposeof using the inhibitor is to prevent the degradation of theproteinaceous medicament. Problems that arise from using proteaseinhibitors to aid in oral delivery of proteinaceous drugs have beenenumerated hereinabove.

International Publications WO 93-02664 (issued February, 1993) andWO94-08610 (issued Apr. 28, 1994) of Constantides et al. describecompositions of w/o microemulsion formulations containing peptides andproteins using medium chain fatty acid triglycerides, surfactants and ahydrophilic phase containing proteins. The ratio of triglycerides to lowHLB surfactants in these preparations can be 5:1 to 1.5:1. Constantideset al. also describe the preparation of microemulsion compositionscontaining salts of medium chain fatty acids (high HLB surfactant) inwhich the insulin loading is 0.35 mg/mL. Contrary to the approach of theinvention hereinafter disclosed, a careful examination of the examplesof the Constantides et al., International Publications WO 93-02664(issued February, 1993) and WO94-08610 (issued Apr. 28, 1994) revealstheir combined HLB strength to be above 7.

It would therefore be a substantial advance in the art, and iscorrespondingly an object of the present invention, to provide animproved formulation for the administration of therapeutic agents suchas proteins, peptides, nucleosides, nucleotides, antiviral agents,antineoplastic agents, antibiotics, antiarrhythmics, anti-coagulants,etc., and prodrugs precursors, derivatives, and intermediates of theforegoing, which avoids the foregoing problems.

It is another object of the invention to provide an improved formulationfor the oral administration of protein and peptide therapeutic agents,in which the therapeutic agent is stabilized against proteolysis anddegradation in the gastrointestinal tract.

It is yet another object of the invention to provide an improvedformulation for administration of therapeutic agents which are of freeform and/or are conjugatively stabilized as described in U.S. Pat. No.5,681,811 issued Oct. 28, 1997, U.S. Pat. No. 5,438,040 issued Aug. 1,1995 and U.S. Pat. No. 5,259,030 issued Oct. 25, 1994, all in the nameof Nnochiri Nkem Ekwuribe.

Other objects and advantages of the present invention will be more fullyapparent from the ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

The present invention relates to microemulsion formulations of free-formand/or conjugation-stabilized therapeutic agents, and to methods ofmaking and using same. The compositions of the invention may comprisetherapeutic agents such as proteins, peptides, nucleosides, nucleotides,antiviral agents, antineoplastic agents, antibiotics, antiarrhythmics,anti-coagulants, etc., and prodrugs, precursors, derivatives, andintermediates thereof.

The formulations of the present invention may utilizeconjugation-stabilized therapeutic and/or diagnostic agent compositions,which are conjugatively stabilized as more fully described in U.S. Pat.No. 5,681,811 issued Oct. 28, 1997, U.S. Pat. No. 5,438,040 issued Aug.1, 1995 and U.S. Pat. No. 5,259,030 issued Oct. 25, 1994, all in thename of Nnochiri Nkem Ekwuribe, the disclosures of which are herebyincorporated herein in their entirety.

More particularly, the formulations of the present invention may utilizecovalently conjugated therapeutic and/or diagnostic complexes whereinthe therapeutic and/or diagnostic agent peptide is covalently bonded toone or more molecules of a polymer incorporating as an integral partthereof a hydrophilic moiety, e.g., a linear polyalkylene glycol, andwherein said polymer incorporates a lipophilic moiety as an integralpart thereof.

In one particular aspect, the present invention relates to a formulationincluding a physiologically active therapeutic agent covalently coupledwith a polymer comprising (i) a linear polyalkylene glycol moiety and(ii) a lipophilic moiety, wherein the therapeutic agent, linearpolyalkylene glycol moiety, and the lipophilic moiety areconformationally arranged in relation to one another such that thephysiologically active therapeutic agent in the formulation has anenhanced in vivo resistance to enzymatic degradation, relative to thephysiologically active therapeutic agent alone (i.e., in an unconjugatedform devoid of the polymer coupled thereto).

In another aspect, the invention relates to a formulation including aphysiologically active therapeutic agent composition ofthree-dimensional conformation comprising a physiologically activetherapeutic agent covalently coupled with a polysorbate complexcomprising (i) a linear polyalkylene glycol moiety and (ii) a lipophilicmoiety, wherein the physiologically active therapeutic agent, the linearpolyalkylene glycol moiety and the lipophilic moiety areconformationally arranged in relation to one another such that (a) thelipophilic moiety is exteriorly available in the three-dimensionalconformation, and (b) the physiologically active therapeutic agent inthe physiologically active therapeutic agent composition has an enhancedin vivo resistance to enzymatic degradation, relative to thephysiologically active therapeutic agent alone.

In a further aspect, the invention relates to formulations including amultiligand conjugated therapeutic agent complex comprising atriglyceride backbone moiety, having:

a bioactive therapeutic agent covalently coupled with the triglyceridebackbone moiety through a polyalkylene glycol spacer group bonded at acarbon atom of the triglyceride backbone moiety; and

at least one fatty acid moiety covalently attached either directly to acarbon atom of the triglyceride backbone moiety or covalently joinedthrough a polyalkylene glycol spacer moiety.

In such multiligand conjugated therapeutic agent complex, the α and βcarbon atoms of the triglyceride bioactive moiety may have fatty acidmoieties attached by covalently bonding either directly thereto, orindirectly covalently bonded thereto through polyalkylene glycol spacermoieties. Alternatively, a fatty acid moiety may be covalently attachedeither directly or through a polyalkylene glycol spacer moiety to the aand a′ carbons of the triglyceride backbone moiety, with the bioactivetherapeutic agent being covalently coupled with the β-carbon of thetriglyceride backbone moiety, either being directly covalently bondedthereto or indirectly bonded thereto through a polyalkylene spacermoiety. It will be recognized that a wide variety of structural,compositional, and conformational forms are possible for the multiligandconjugated therapeutic agent complex comprising the triglyceridebackbone moiety, within the scope of the foregoing discussion.

In such a multiligand conjugated therapeutic agent complex, thebioactive therapeutic agent may advantageously be covalently coupledwith the triglyceride modified backbone moiety through alkyl spacergroups, or alternatively other acceptable spacer groups, within thebroad scope of the invention. As used in such context, acceptability ofthe spacer group refers to steric, compositional, and end useapplication specific acceptability characteristics.

In yet another aspect, the invention relates to a formulation includinga polysorbate complex comprising a polysorbate moiety including atriglyceride backbone having covalently coupled to a, a′ and β carbonatoms thereof functionalizing groups including:

(i) a fatty acid group; and

(ii) a polyethylene glycol group having a physiologically active moietycovalently bonded thereto, e.g., a physiologically active moiety iscovalently bonded to an appropriate functionality of the polyethyleneglycol group.

Such covalent bonding may be either direct, e.g., to a hydroxy terminalfunctionality of the polyethylene glycol group, or alternatively, thecovalent bonding may be indirect, e.g., by reactively capping thehydroxy terminus of the polyethylene glycol group with a terminalcarboxy functionality spacer group, so that the resulting cappedpolyethylene glycol group has a terminal carboxy functionality to whichthe physiologically active moiety may be covalently bonded.

The invention relates to a further aspect to a formulation including astable, aqueously soluble, conjugated therapeutic agent complexcomprising a physiologically active therapeutic agent covalently coupledto a physiologically compatible polyethylene glycol modified glycolipidmoiety. In such complex, the physiologically active therapeutic agentmay be covalently coupled to the physiologically compatible polyethyleneglycol modified glycolipid moiety by a labile covalent bond at a freeamino acid group of the therapeutic agent, wherein the labile covalentbond may be scissionable in vivo by biochemical hydrolysis and/orproteolysis. The physiologically compatible polyethylene glycol modifiedglycolipid moiety may advantageously comprise a polysorbate polymer,e.g., a polysorbate polymer comprising fatty acid ester groups selectedfrom the group consisting of monopalmitate, dipalmitate, monolaurate,dilaurate, trilaurate, monoleate, dioleate, trioleate, monostearate,distearate, and tristearate. In such complex, the physiologicallycompatible polyethylene glycol modified glycolipid moiety may suitablycomprise a polymer selected from the group consisting of polyethyleneglycol ethers of fatty acids, and polyethylene glycol esters of fattyacids, wherein the fatty acids for example comprise a fatty acidselected from the group consisting of lauric, palmitic, oleic, andstearic acids.

In the above complex, the physiologically active therapeutic agent mayillustratively comprise a peptide, protein, nucleoside, nucleotide,antineoplastic, agent, antibiotic, anticoagulant, antiarrhythmic agent,antiviral agent, or prodrugs, precursors, intermediates, or derivativesthereof.

For example, the therapeutic agent may comprise peptide selected fromthe group consisting of insulin, calcitonin, ACTH, glucagon,somatostatin, somatotropin, somatomedin, parathyroid hormone,erythropoietin, hypothalmic releasing factors, prolactin, thyroidstimulating hormones, endorphins, enkephalins, vasopressin,non-naturally occurring opioids, superoxide dismutase, interferon,asparaginase, arginase, arginine deaminease, adenosine deaminaseribonuclease, trypsin, chemotrypsin, and papain.

As other examples, the therapeutic agent may comprise: An antiviral suchas: Ara-A (Arabinofuranosyladenine), Acylguanosine, Nordeoxyguanosine,Azidothymidine, Dideoxyadenosine, or Dideoxycytidine; an anti-canceragent such as Dideoxyinosine Floxuridine, 6-Mercaptopurine, Doxorubicin,Daunorubicin, or I-darubicin; and antibiotic such as Erythormycin,Vancomycin, oleandomycin, or Ampicillin; an antiarrhythmic such asQuinidine; or an anticoagulant such as Heparins.

In another aspect, the present invention relates to an oraladministration dosage form for the mediation of insulin deficiency,comprising a formulation including a pharmaceutically acceptable carrierand a stable, aqueously soluble, conjugated insulin complex comprisinginsulin or proinsulin covalently coupled to a physiologically compatiblepolyethylene glycol modified glycolipid moiety.

In a further aspect, the invention relates to a method of treatinginsulin deficiency in a human or non-human mammalian subject exhibitingsuch deficiency, comprising orally administering to the subject aneffective amount of a conjugated insulin composition comprising astable, aqueously soluble, conjugated insulin complex comprising insulincovalently or proinsulin covalently coupled to a physiologicallycompatible polyethylene glycol modified glycolipid moiety.

The term “peptide” as used herein is intended to be broadly construed asinclusive of polypeptides per se having molecular weights of up to about10,000, as well as proteins having molecular weights of greater thanabout 10,000, wherein the molecular weights are number average molecularweights. As used herein, the term “covalently coupled” means that thespecified moieties are either directly covalently bonded to one another,or else are indirectly covalently joined to one another through anintervening moiety or moieties, such as a bridge, spacer, or linkagemoiety or moieties. The term “conjugatively coupled” means that thespecified moieties are either covalently coupled to one another or theyare non-covalently coupled to one another, e.g., by hydrogen bonding,ionic bonding, Van der Waals forces, etc. The term “free” in referenceto a therapeutic agent means that the therapeutic agent is notconjugatively coupled in the specific formulation. The term “therapeuticagent” means an agent which is therapeutically useful, e.g., an agentfor the treatment, remission or attenuation of a disease state,physiological condition, symptoms, or etiological factors, or for theevaluation or diagnosis thereof.

As used herein, the term “hydrophilic and lipophilic balance” or “HLB”means a value determined in accordance with the method described in P.Becher et al., “Nonionic Surfactant, Physical Chemistry,” Marcel Dekker,New York (1987), pages 439-456. The HLB value is an empirical value onan arbitrary scale that is conveniently and widely used in surfactantchemistry to provide a measure of the polarity of a surfactant ormixture of surfactants, as for example is referenced in U.S. Pat. No.5,646,109 (issued Jul. 8, 1997). As noted in such patent at column 16,lines 24-27 thereof, HLB values are commonly provided by surfactantsuppliers, and HLB values for a mixture of surfactants are calculated ona volumetric basis. See also U.S. Pat. No. 5,206,219 (issued Apr. 27,1993) at column 5, lines 3-17, giving illustrative examples of HLBvalues for various esters of polyethylene glycol, polyethylene fattyacid esters and polyoxyethylated fatty acids.

The invention thus comprehends various compositions for therapeutic (invivo) application, wherein the therapeutic agent component of theconjugated therapeutic agent complex is a physiologically active, orbioactive, therapeutic agent. In such therapeutic agent-containingcompositions, the conjugation of the therapeutic agent component to thepolymer comprising hydrophilic and lipophilic moieties may be directcovalent bonding or indirect (through appropriate spacer groups)bonding, and the hydrophilic and lipophilic moieties may also bestructurally arranged in the polymeric conjugating structure in anysuitable manner involving direct or indirect covalent bonding, relativeto one another. Thus, a wide variety of therapeutic agent species may beaccommodated in the broad practice of the present invention, asnecessary or desirable in a given end use therapeutic application.

In another aspect, covalently coupled therapeutic agent compositionssuch as those described above may utilize therapeutic agent componentsintended for diagnostic or in vitro applications, wherein thetherapeutic agent is for example a diagnostic reagent, or a complementof a diagnostic conjugate for immunoassay or other diagnostic or non-invivo applications. In such non-therapeutic applications, the complexesof the invention are highly usefully employed as stabilized compositionswhich may for example be formulated as hereinafter more fully describedwith compatible solvents or other solution-based formulations to providestable compositional forms which are of enhanced resistance todegradation.

In the foregoing therapeutic and non-therapeutic (e.g., diagnostic)applications, the present invention relates in one broad compositionalaspect to formulations including covalently conjugated therapeutic agentcomplexes wherein the therapeutic agent is covalently bonded to one ormore molecules of a polymer incorporating as an integral part of saidpolymer a hydrophilic moiety, e.g., a polyalkylene glycol moiety, and alipophilic moiety, e.g., a fatty acid moiety. In one preferred aspect,the therapeutic agent may be covalently conjugated by covalent bondingwith one or more molecules of a linear polyalkylene glycol polymerincorporated in which, as an integral part thereof is a lipophilicmoiety, e.g., a fatty acid moiety.

In another broad aspect, the present invention relates to formulationsof non-covalently conjugated therapeutic agent complexes wherein thetherapeutic agent is non-covalently associated with one or moremolecules of a polymer incorporating as an integral part thereof ahydrophilic moiety, e.g., a polyalkylene glycol moiety, and a lipophilicmoiety, e.g., a fatty acid moiety. The polymer may be variouslystructured and arranged analogous to description of the polymer in thecovalently conjugated therapeutic agent complexes described above, butwherein the therapeutic agent is not bonded to the polymer molecule(s)in a covalent manner, but is nonetheless associated with the polymer, asfor example by associative bonding, such as hydrogen bonding, ionicbonding or complexation, Van der Waals bonding, micellular encapsulationor association (of the specific therapeutic agent), etc., oralternatively wherein the therapeutic agent is in a free form in theformulation, unassociated with any conjugating polymer.

In associatively conjugated therapeutic agent compositions of theabove-described type, the polymer component may be suitably constructed,modified, or appropriately functionalized to impart the ability forassociative conjugation in a selectively manner (for example, to imparthydrogen bonding capability to the polymer viz-a-vis the therapeuticagent), within the skill of the art.

The formulations of therapeutic agent component(s) and polymericmoiety/(ies) within the broad scope of the present invention may forexample utilize a therapeutic agent component for therapeutic (e.g., invivo) applications, as well as non-therapeutic therapeutic agentcomponents, e.g., for diagnostic or other (in vitro) use.

The formulations of the present invention advantageously comprise amicroemulsion of a therapeutic agent in free and/or conjugativelycoupled form, wherein the microemulsion has a hydrophilic and lipophilicbalance (HLB) value of between 3 and 7, more preferably from about 5 toabout 6.5 and most preferably from about 5 to about 6. The microemulsionsuitably comprises a water-in-oil (w/o) emulsion of such characterhaving a clear optical character.

In a specific aspect, the present invention relates to an oral dosageform of insulin. Such insulin may be in the free state and/orconjugatively coupled with an amphiphilic polymer (the conjugativecoupling may be covalent coupling and/or associative (non-covalent)coupling).

The present invention also relates to a method by which the insulinconjugates and/or free insulin may be prepared in microemulsionformulation.

The present invention provides a safe and effective oral dosage formapplicable to free insulin and/or insulin conjugates, as well as toother therapeutic agents, e.g., proteinaceous medicaments, in free formand/or modified by amphiphilic polymers for the purpose of enhancingtheir stability for oral administration. Unmodified therapeutic agentsthat are amphiphilic in character can also be usefully employed in thebroad practice of the present invention.

The present invention differs from the composition and method ofpreparation of other known microemulsions. As discussed in the“Background of the Invention” section hereof, the current state of theart recognizes the instability of protein drugs in the gastrointestinaltract and has endeavored to circumvent such problem by formulatingprotein drugs with protease inhibitors.

Such protease inhibitors by their intrinsic character function toprotect harmful proteinaceous material in the tract from degradation,and the added protease inhibitors thereby interfere with natural anddesirable physiological digestive processes. The presence of proteaseinhibitors in oral formulations may therefore have quite seriousconsequences to the health and well-being of the patient. The presentinvention contemplates the use of therapeutic formulations in which thetherapeutic agent(s) can be usefully and effectively stabilized withoutprotease inhibitors and their attendant problems.

The microemulsion formulation of the present invention provides a dosageform for the safe and effective oral administration of (i) the free formof therapeutic agents such as insulin, (ii) amphiphilic conjugates ofsuch therapeutic agents, or (iii) mixtures of such free form therapeuticagents and their conjugates.

The method of the invention for preparing microemulsion formulationsuseful as oral dosage forms of therapeutic agents such as insulin,utilizes emulsification techniques in a novel fashion with respect tothe selection of oil, water and cosurfactant components, to provide amicroemulsion having a specific HLB character useful for oral drugdelivery. The oil component of the microemulsion formulation of theinvention appropriately comprises a pharmaceutically acceptable oil,preferably of a food grade quality.

In reference to insulin, the selection of oil, water and cosurfactantconstituents to yield a microemulsion having an HLB value of less than 7provides a stable formulation for incorporating free form insulin and/orinsulin conjugates for effective oral administration of the insulin.

In the insulin formulations of the invention, particularly preferredinsulin forms include the so-called hex-insulin mixture hereinafterdisclosed, which is amphiphilic and able to distribute well in oil,surfactant and water. The hex-insulin mixture is formed from insulinconjugated with a hexyl polymer which forms a mixture of mono-, di- andtri-conjugates of insulin as well as free insulin as the conjugativereaction product (the mono-, di- and tri- prefixes referring to thenumber of polymer moieties attached to the insulin molecule).

The hex-insulin mixture is more stable than unconjugated insulin againstproteolytic digestion (Table B). In closed loop assay determinations(FIGS. 3, 4), the hex-insulin mixture is better absorbed thanunconjugated insulin and gives better glucose reduction than insulin (onan insulin weight basis). In the microemulsion formulation of thepresent invention, the concentration of the hex-insulin mixture in theformulation is able to be increased above the concentration possible forfree zinc insulin alone, and the formulation of both the hex-insulinmixture and free zinc insulin in the microemulsion compositions of thepresent invention shows improved absorption of the hex-insulin mixturein relation to absorption of zinc insulin (FIG. 6). Accordingly, thehex-insulin mixtures of the invention are highly efficacious inproviding superior absorption of the insulin component and concomitantreduction of blood glucose in therapeutic use.

When used in free form in the formulations of the present invention, theinsulin may be used in any suitable form, such as in salt forms such aszinc insulin, sodium insulin, etc. or other pharmaceutically acceptableforms of insulin.

While the invention is described hereinafter primarily with respect tothe preferred oral administration use of the formulation of theinvention, the formulation of the invention may also be used forparenteral administration or any other suitable mode of administration.

Other aspects, features, and modifications of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of serum glucose, in mg/dL, as a function of time, inminutes, for administration of insulin per se and in complexed forms.

FIG. 2 is a graph of serum glucose, in mg/dL, as a function of time, inhours, for administration of insulin in various forms.

FIG. 3 is a graph of ELISA assay results for native insulin in the NRSpool of various Sprague-Dawley rats, showing insulin concentration as afunction of time, prior to and after dosing with insulin, at respectivedoses of 10 milligrams of insulin per kilogram of body weight, and at 30milligrams of insulin per kilogram of body weight.

FIG. 4 is a graph of ELISA assay results for insulin in the NRS pool ofvarious Sprague-Dawley rats, showing insulin concentration as a functionof time, prior to and after dosing with insulin, at respective doses of10 milligrams of insulin per kilogram of body weight, and at 30milligrams of insulin per kilogram of body weight, wherein the insulinis administered as a conjugate, insulin-hexyl-PEG₇-OMe.

FIG. 5 is a graph of percent of pre-dose blood glucose level as afunction of time, for free insulin, and for conjugated insulin atrespective doses of 1, 3 and 10 milligrams of insulin per kilogram ofbody weight, against a control of phosphate buffered solution (PBS) andbovine serum albumen (BSA) in various Sprague Dawley rats.

FIG. 6 is a graph of insulin and blood glucose levels in pancreatomizeddogs as a function of time, after dosing with a microemulsion insulinformulation representative of the present invention.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

The disclosures of the following United States Patents are herebyincorporated herein in their entirety: U.S. Pat. No. 5,681,811 issuedOct. 28, 1997, U.S. Pat. No. 5,438,040 issued Aug. 1, 1995 and U.S. Pat.No. 5,259,030 issued Oct. 25, 1994, all in the name of Nnochiri NkemEkwuribe.

Modification of therapeutic agents with non-toxic, non-immunogenicpolymers affords certain advantages. If modifications are made in such away that the products (polymer-therapeutic agent conjugates) retain allor most of their biological activities the following properties mayresult: epithelial penetration capability may be enhanced; the modifiedtherapeutic agent may be protected from proteolytic digestion andsubsequent abolition of activity; affinity for endogenous transportsystems may be improved; chemical stability against stomach acidity maybe imparted; and the balance between lipophilicity and hydrophobicity ofthe polymers may be optimized. Proteinaceous substances endowed with theimproved properties described above can be effective as replacementtherapy following either oral or parenteral administration. Other routesof administration, such as nasal and transdermal, are potentiallyadvantageously employed with the modified therapeutic agent.

In non-therapeutic (e.g., diagnostic) applications,conjugation-stabilization of diagnostic and/or reagent species ofpeptides, nucleosides, or other therapeutic agents, including precursorsand intermediates of end-use nucleosides, peptides or other products,provides corresponding advantages, when the conjugation component iscovalently bonded to a polymer as hereinafter disclosed. The resultinglycovalently conjugated agent is resistant to environmental degradativefactors, including solvent- or solution-mediated degradation processes.As a result of such enhanced resistance to degradation, the shelf lifeof the active ingredient is able to be significantly increased, withconcomitant reliability of the therapeutic agent-containing compositionin the specific end use for which same is employed.

The covalent conjugation of therapeutic agents with polymers in themanner of the present invention effectively minimizes hydrolyticdegradation, and achieves in vitro and in vivo stabilization.

Analogous benefits are realized when therapeutic, diagnostic, or reagentspecies are non-covalently, associatively conjugated with polymermolecule(s) in the manner of the present invention.

Additionally, the formulation of the present invention may utilize thetherapeutic agent in a free form, as previously described.

The formulations of the invention may utilize the therapeutic agent inany suitable combination or permutation of the foregoing forms(covalently conjugated, associatively conjugated, and/or free form(unconjugated)).

Utilizing a peptide covalently bonded to the polymer component as anillustrative embodiment of the form of the therapeutic agent used in thepractice of the invention, the nature of the conjugation, involvingcleavable covalent chemical bonds, allows for control in terms of thetime course over which the polymer may be cleaved from the peptide(insulin). This cleavage may occur by enzymatic or chemical mechanisms.The conjugated polymer-peptide complex will be intrinsically active.Full activity will be realized following enzymatic cleavage of thepolymer from the peptide. Further, the chemical modification will allowpenetration of the attached peptide, e.g., insulin, through cellmembranes.

In a preferred aspect of the present invention when the therapeuticagent is employed in a conjugated form, membrane penetration-enhancingproperties of lipophilic fatty acid residues are incorporated into thebody of the conjugating polymer. In this respect, again utilizinginsulin as the peptide of interest, fatty acid polymer derivatives ofinsulin improve the intestinal absorption of insulin: carbamylation ofthe amino groups of Phe^(B1) and Lys^(B29) with long-chain fatty acidpolymers yield compounds which provide some degree of hypoglycemicactivity. This derivatization increases the stability of insulin inintestinal mucosa and its absorption from the small intestine.

While the ensuing description is primarily and illustratively directedto the use of insulin as a peptide component in various compositions andformulations of the invention, it will be appreciated that the utilityof the invention is not thus limited, but rather extends to any specieswhich are useful in free form or covalently or associativelyconjugatable, for use in microemulsion formulations in the manner of theinvention, including, but not limited to: the following peptide species:calcitonin, ACTH, glucagon, somatostatin, somatotropin, somatomedin,parathyroid hormone, erythropoietin, hypothalmic releasing factors,prolactin, thyroid stimulating hormone, endorphins, antibodies,hemoglobin, soluble CD-4, clotting factors, tissue plasminogenactivator, enkephalins, vasopressin, non-naturally occurring opioids,superoxide dismutase, interferon, asparaginase, arginase, argininedeaminease, adenosine deaminase ribonuclease, trypsin, chemotrypsin, andpapain, alkaline phosphatase, and other suitable enzymes, hormones,proteins, polypeptides, enzyme-protein conjugates, antibody-haptenconjugates, viral epitopes, etc.; antivirals such as: Ara-A(Arabinofuranosyladenine), Acylguanosine, Nordeoxyguanosine,Azidothymidine, Dideoxyadenosine, and Dideoxycytidine; anti-canceragents such as Dideoxyinosine Floxuridine, 6-Mercaptopurine,Doxorubicin, Daunorubicin, and I-darubicin; and antibiotic such asErythormycin, Vancomycin, oleandomycin, and Ampicillin; antiarrhythmicssuch as Quinidine; and anticoagulants such as Heparins.

In the practice of the present invention when the therapeutic agent isemployed in a conjugated form, suitable polymers for conjugation withthe therapeutic agents are employed so as to obtain the desirablecharacteristics enumerated above. Such modified therapeutic agents maybe employed for sustained in vivo delivery of the therapeutic agent.

The present invention provides microemulsion formulations for deliveryof therapeutic agents orally in their active form. The invention mayalso be practiced with amphiphilic prodrugs that are therapeuticallyeffective by oral or parenteral administration.

Within the broad scope of the present invention, microemulsionformulations are provided including agents useful for therapeuticapplications, as well as immunoassay, diagnostic, and othernon-therapeutic (e.g., in vitro) applications. The formulations of thepresent invention may be employed to provide stabilized peptide andnucleoside compositions variously suitable for in vivo as well as non-invivo applications, wherein the peptide and nucleoside agents may beconjugated and/or unconjugated in character.

Within the broad scope of the present invention, when the therapeuticagent employed in the formulation is conjugated, a single polymermolecule may be employed for conjugation with a plurality of therapeuticagent species, and it may also be advantageous in the broad practice ofthe invention to utilize a variety of polymers as conjugating agents fora given therapeutic agent; combinations of such approaches may also beemployed. Further, it will be recognized that the conjugating polymer(s)may utilize any other groups, moieties, or other conjugated species, asappropriate to the end use application. By way of example, it may beuseful in some applications to covalently bond to the polymer afunctional moiety imparting UV-degradation resistance, or antioxidantcharacter, or other properties or characteristics to the polymer. As afurther example, it may be advantageous in some applications tofunctionalize the polymer to render same reactive or cross-linkable incharacter, to enhance various properties or characteristics of theoverall conjugated material. Accordingly, the polymer may contain anyfunctionality, repeating groups, linkages, or other constituentstructures which do not preclude the efficacy of the conjugatedcomposition for its intended purpose.

Illustrative polymers that may usefully be employed achieve thesedesirable characteristics are described herein below in an exemplaryreaction scheme. In covalently bonded peptide applications, the polymersmay be functionalized and then coupled to free amino acid(s) of thepeptide(s) to form labile bonds which permit retention of activity withthe labile bonds intact. Removal of the bond by chemical hydrolysis andproteolysis then enhances the peptidal activity.

The polymers utilized in the invention, when the therapeutic agentemployed in the formulation is conjugated, may suitably incorporate intheir molecules constituents such as edible fatty acids (lipophilicend), polyethylene glycols (water soluble end), acceptable sugarmoieties (receptor interacting end), and spacers for therapeutic agentattachment. Among the polymers of choice, polysorbates are particularlypreferred and are chosen to illustrate various embodiments of theinvention in the ensuing discussion herein. The scope of this inventionis of course not limited to polysorbates, and various other polymersincorporating above-described moieties may usefully be employed in thebroad practice of this invention. Sometimes it may be desirable toeliminate one of such moieties and to retain others in the polymerstructure, without loss of objectives. When it is desirable to do so,the preferred moieties to eliminate without losing the objectives andbenefits of the invention are the sugar and/or the spacer moieties.

It is preferred to operate with conjugating polymers whose molecularweights are in the range of between 120 and 10,000 daltons.

In the practice of the present invention, polyalkylene glycol residuesof C₂-C₄ alkyl polyalkylene glycols, preferably polyethylene glycol(PEG), are advantageously incorporated in the polymer systems ofinterest.

The presence of these PEG residues will impart hydrophilic properties tothe polymer and to the corresponding polymer-therapeutic agentconjugates. Certain glycolipids are known to stabilize therapeuticagents such as proteins and peptides. The mechanism of thisstabilization probably involves association of the glycolipid fatty acidmoieties with the hydrophobic domain of the peptide or protein;aggregation of the protein or peptide is thus prevented. It also isknown that aggregated peptides are poorly absorbed in the smallintestine compared to native peptides. The invention thereforecontemplates polymer-peptide conjugation products in which the peptide,e.g., insulin, is conjugated with either the hydrophilic or hydrophobicresidue of the polymer. The fatty acid portion of the polymer isprovided to associate with the hydrophobic domain of the peptide andthus prevent aggregation in solution. The resulting polymer-peptideconjugates thus will be: stabilized (to chemical and enzymatichydrolysis); water-soluble, due to the PEG residue; and, by virtue ofthe fatty acid-hydrophobic domain interactions, not prone toaggregation.

Polyalkylene glycol derivatization has a number of advantageousproperties in the formulation of polymer-therapeutic agent conjugates inthe practice of the present invention, as associated with the followingproperties of polyalkylene glycol derivatives: improvement of aqueoussolubility, while at the same time eliciting no antigenic or immunogenicresponse; high degrees of biocompatibility; absence of in vivobiodegradation of the polyalkylene glycol derivatives; and ease ofexcretion by living organisms.

The polymers employed in the practice of the present invention asconjugating components of the inventive formulation thus compriselipophilic and hydrophilic moieties, rendering the resultingpolymer-drug conjugate highly effective (bioactive) in oral as well asparenteral and other modes of physiological administration. As usedhereinafter, the terms “drug” and “therapeutic agent” are usedinterchangeably.

Set out below as illustrative examples of polymer-therapeutic agentconjugates of the present invention are the formulae of covalentlybonded conjugates denoted for ease of subsequent reference as Conjugate1, Conjugate 2, and Conjugate 3, wherein “drug” is insulin or othertherapeutic agent, and specific values of m, n, w, x, and y will bedescribed in the ensuing discussion.

Conjugate 1

R=C₄-C₂₀; n=1 to 125

or other fatty acid radicals from C₄-C₂₀.

Conjugate 2

wherein: m and n each are independently from 1 to 125.

Conjugate 3

wherein: m and n each are independently from 1 to 125.

Conjugate 1 features commercially available polysorbate monooleate atthe center of the polymeric system, a sugar derivative used in manypharmaceutical applications. Lipophilic and absorption enhancingproperties are imparted by the fatty acid chain, while the polyethyleneglycol (PEG) residues provide a hydrophilic (hydrogen bond accepting)environment. Drug is attached through a carbamate linkage adjacent tothe PEG region of the polymer.

In Conjugate 2 the sugar residue is excluded, but drug is once againattached to the polymer through a carbamate bond adjacent to thehydrophilic PEG region of the polymer. The lipophilic fatty acid regionof the polymer is thus some distance from the point of attachment todrug, e.g., insulin.

The arrangement described above for Conjugate 2 is reversed in the caseof Conjugate 3. Once more the sugar residue is excluded, but in thisstructure the lipophilic fatty acid residue is closest to the point ofattachment to drug and the hydrophilic PEG region is distant from thepoint of attachment, which again is through a carbamate bond.

Varied alignments of hydrophilic and lipophilic regions relative to thepoint of attachment of the polymer to the drug are possible in the broadpractice of the invention, and such variation will result in polymerswhich provide lipophilic and hydrophilic domains to the drug. InConjugates 1, 2, and 3 the point of attachment of the carbamate bondbetween the polymers is preferably the amine function.

In the general practice of the invention, various methods of couplingthe polymers to the therapeutic agent, e.g., peptide, nucleoside, etc.are available and are discussed more fully hereinafter.

The polymers utilized in therapeutic agent conjugation in accordancewith the invention are designed to incorporate good physicalcharacteristics that enable them to achieve the desired objectives.Absorption enhancers, while enabling penetration of the drug through thecell membrane, do not improve the stability characteristics of the drug,and in vivo applications may therefore utilize the polymer-drugconjugates of the invention in formulations devoid of such penetrationenhancers. One aspect of the present invention therefore relates to theincorporation of fatty moiety within the polymer, to mimic penetrationenhancers. The microemulsion formulations of the invention arepreferably devoid of any protease inhibitors. Protease inhibitors havebeen used in the prior art to enhance the stability of proteinaceoustherapeutic agents, as herein earlier discussed, but are desirablyabsent in the microemulsion formulations of the present invention.

In the covalently conjugated polymer-therapeutic agent conjugates of thepresent invention, the drug may be covalently attached to thewater-soluble polymer by means of a labile chemical bond. This covalentbond between the drug and the polymer may be cleaved by chemical orenzymatic reaction. The polymer-drug product retains an acceptableamount of activity; full activity of the component drug is realized whenthe polymer is completely cleaved from the drug. Concurrently, portionsof polyethylene glycol are present in the conjugating polymer to endowthe polymer-drug conjugate with high aqueous solubility and prolongedblood circulation capability. The modifications described above conferimproved solubility, stability, and membrane affinity properties on thedrug. As a result of these improved characteristics the inventioncontemplates parenteral and oral delivery of both the activepolymer-drug species and, following hydrolytic cleavage, bioavailabilityof the drug per se, in in vivo applications.

The polymers used in the embodiment described below can be classified aspolyethylene glycol modified lipids and polyethylene glycol modifiedfatty acids. Among preferred conjugating polymers may be mentionedpolysorbates comprising monopalmitate, dipalmitate, tripalmitate,monolaurate, dilaurate, trialaurate, monooleate, dioleate, trioleate,monostearate, distearate, and tristearate. Other lower fatty acids canbe utilized. The number average molecular weight of polymer resultingfrom each combination is preferred to be in the range of from about 750to about 5,000 daltons. Alternative polymers of preference arepolyethylene glycol ethers or esters of fatty acids, such fatty acidsbeing lauric, palmitic, oleic, and stearic acids, and other lower fattyacids can be utilized, with the polymers ranging from 250 to 5,000daltons in number average molecular weight. It is preferred to have aderivatizable group in the polymer, where such group can be at the endterminating with polyethylene glycol or at the end terminating withfatty moiety. The derivatizable group may also be situated within thepolymer and thus may serve as a spacer between the peptide (or othertherapeutic agent) and the polymer.

Several methods of modifying fatty acid sorbitan to achieve the desiredpolymer will be discussed in further detail with structuralillustrations. Polysorbates are esters of sorbitols and theiranhydrides, which are copolymerized with ethylene oxide. Shown below isthe structure of a representative polymer.

The sum of w, x, y, z is 20 and R₁, R₂ and R₃ are each independentlyselected from the group consisting of lauric, oleic, palmitic andstearic acid radicals, or R₁ and R₂ are each hydroxyl while R₃ islauric, palmitic, oleic or stearic acid radical, or lower fatty acid.These polymers are commercially available and are used in pharmaceuticalformulations. Where a higher molecular weight polymer is desired, it maybe synthesized from glycolipids such as sorbitan monolaurate, sorbitanmonooleate, sorbitan monopalmitate or sorbitan monostearate, and anappropriate polyethylene glycol. Structures of glycolipids which may beused as starting reagents are depicted below.

In the synthesis of glycolipid polymers substituted in three positionswith polyethylene glycol, a desired polyethylene glycol having two freehydroxyls at the termini is protected at one terminus with a tritylgroup in pyridine using one mole of trityl chloride. The remaining freehydroxyl group of the polyethylene glycol is converted to eithertosylate or bromide. The desired glycolipid is dissolved in a suitableinert solvent and treated with sodium hydride. The tosylate or bromideof the protected polyethylene glycol is dissolved in inert solvent andadded in excess to the solution of glycolipid. The product is treatedwith a solution of para-toluenesulfonic acid in anhydrous inert solventat room temperature and purified by column chromatography. Thestructures of the transformation are depicted below.

By adjusting the molar equivalent of reagents and using the appropriatemolecular weight range of polyethylene glycol, mono or disubstitutedglycolipids of the desired molecular weight range can be obtained byfollowing the above procedures.

wherein each n and m may vary independently, and have any suitable valueappropriate to the specific drug being stabilized, e.g., from 1 to 16.

The sugar portion of the glycolipid described above can be substitutedwith glycerol or aminoglycerol whose structural formulae are shownbelow.

In this modification, the primary alcohol is first etherified oresterified with a fatty acid moiety such as lauric, oleic, palmitic orstearic; the amino group is derivatized with fatty acids to form amidesor secondary amino groups, as shown below.

wherein m may have any suitable value, e.g., from 10 to 16.

The remaining primary alcohol group is protected with a trityl groupwhile the secondary alcohol group is converted with polyethylene glycolto a desired polymer. Usually, the polyethylene glycol bears a leavinggroup at one terminal and a methoxy group at the other terminal. Thepolyethylene glycol is dissolved in inert solvent and added to asolution containing glycolipid and sodium hydride. The product isdeprotected in para-toluenesulfonic acid at room temperature to give thedesired polymer as depicted.

Sometimes it is desirable to incorporate fatty acid derivatives indifferent parts of the polyethylene glycol chain to achieve certainphysicochemical properties similar to polysorbates that have beensubstituted with two/three molecules of fatty acids, e.g., polysorbatetrioleate.

Structures representing the polymers are shown in the reaction schemebelow as the open chain of the polysorbate.

In the synthesis of polymer A, it is desirable to protect the hydroxylmoieties on the first and second carbon of glycerol, e.g. solketal. Theremaining hydroxyl group is converted to the sodium salt in an inertsolvent and reacted with halogenated or tosylated polyethylene glycol inwhich one end of the polyethylene glycol has been protected as an ester.The glycerol protection is removed and the resulting two free hydroxylgroups are converted to the corresponding sodium salts. These salts arereacted in inert solvent with polyethylene glycol which has beenpartially derivatized with fatty acids. Reaction takes place after thefree hydroxyl is converted to the tosylate or bromide.

Polymer G is synthesized in the same manner except that the protectedglycerol is first reacted with esters of fatty acids which have beenhalogenated at the terminal carbon of the acid.

In the synthesis of polymer C, it is preferable to start with 1,3-dihalo-2-propanol. The dihalo compound is dissolved in inert solventand treated with the sodium salt of two moles of polyethylene glycolwhich has been previously derivatized with one mole of a fatty acidmoiety. The product is purified by chromatography or dialysis. Theresulting dry product is treated, in inert solvent, with sodium hydride.The sodium salt thus formed is reacted with a halo derivative ofpartially protected polyethylene glycol.

Sometimes it may be desired to omit the sugar portion of the polymer.The resulting polymer still contains a polyethylene glycol fragment. Themembrane affinity properties of the fatty acid moiety may be retained bysubstituting a fatty acid proper with a lipophilic long chain alkane;biocompatibility is thus preserved. In one instance of this embodimentthe polyethylene glycol with two terminal free hydroxyl groups istreated with sodium hydride in inert solvent. One equivalent weight of aprimary bromide derivative of a fatty acid-like moiety is added to thepolyethylene glycol solvent mixture. The desired product is extracted ininert solvent and purified by column chromatography if necessary.

Where it is desired to form an ester linkage between the fatty acid andthe polyethylene glycol, the acid chloride of the acid is treated withexcess of desired polyethylene glycol in suitable inert solvent. Thepolymer is extracted in inert solvent and further purified bychromatography if necessary.

In some modifications of peptides, it is desired to conjugate the fattyacid moiety directly to the therapeutic agent. In this case the polymeris synthesized with the derivatizable function placed on the fatty acidmoiety. A solution of mono-methoxypolyethylene glycol of appropriatemolecular weight in inert solvent is treated with sodium hydridefollowed by the addition of solution containing the ethyl ester of afatty acid bearing a leaving group at the terminal carbon of the acid.The product is purified after solvent extraction and if necessary, bycolumn chromatography.

The ester protection is removed by treating with dilute acid or base.

Where it is desired to form a carbamate bond with the drug, the carboxylor ester is converted to a hydroxyl group by a chemical reduction methodknown in the art.

HO—(CH₂)_(m)—(OC₂H₄)_(n)XR   (Formula 13)

The functional groups that are used in the drug conjugation are usuallyat a terminal end of the polymer, but in some cases, it is preferredthat the functional group is positioned within the polymer. In thissituation, the derivatizing groups serve as spacers. In one instance ofthis embodiment, a fatty acid moiety may be brominated at the carbonalpha to the carboxylic group and the acid moiety is esterified. Theexperimental procedure for such type of compound is similar to the oneoutlined above, resulting in the product shown below.

When an extended spacer is desired, a polyethylene glycol monoether maybe converted to an amino group and treated with succinic anhydride thathas been derivatized with a fatty acid moiety. A desired polyethyleneglycol bearing primary amine is dissolved in sodium phosphate buffer atpH 8.8 and treated with a substituted succinic anhydride fatty acidmoiety as shown in the scheme below. The product is isolated by solventextraction and purified by column chromatography if necessary.

It is to be understood that the above reaction schemes are provided forthe purposes of illustration only and are not to be limitingly construedin respect of the reactions and structures which may be beneficiallyutilized in the modification of the drug in the broad practice of thepresent invention, e.g., to achieve solubility, stabilization, and cellmembrane affinity for parenteral and oral administration.

The reaction of the polymer with the drug to obtain covalentlyconjugated products is readily carried out. For the purpose of brevityin discussion herein, the polymer is referred to as (P). Where thepolymer contains a hydroxyl group, it is first converted to an activecarbonate derivative such as para-nitrophenyl carbonate. The activatedderivative then is reacted with the amino residue of the drug in a shortperiod of time under mild conditions producing carbamate derivatives.

The above reaction and reagent only serve as illustration and are notexclusive; other activating reagents resulting in formation of urethane,or other, linkages can be employed. The hydroxyl group can be convertedto an amino group using reagents known in the art. Subsequent couplingwith drug through their carboxyl groups results in amide formation.

Where the polymer contains a carboxyl group, it can be converted to amixed anhydride and reacted with the amino group of the drug to create aconjugate containing an amide bond. In another procedure, the carboxylgroup can be treated with water-soluble carbodimide and reacted with thedrug to produce conjugates containing amide bonds.

The activity and stability of the drug conjugates can be varied inseveral ways, by using a polymer of different molecular size.Solubilities of the conjugates can be varied by changing the proportionand size of the polyethylene glycol fragment incorporated in the polymercomposition. Hydrophilic and hydrophobic characteristics can be balancedby careful combination of fatty acid and polyethylene glycol moieties.

Set out below are some illustrative modification reactions forpolymer-drug conjugates of the present invention.

In the above reaction scheme involving species I, J and K, routes aredemonstrated for modifying the hydrophilicity/lipophilicity balance ofthe conjugating polymer. Ester groups in the conjugating polymer aresusceptible to hydrolysis by esterases; the conjugating polymercontaining ester groups therefore may be modified to convert the estergroups to ether groups which are more hydrolysis-resistant in character.The reaction scheme involving L and M species illustrates the conversionof hydroxyl groups to carboxylate groups. In this respect, the carboxylgroups will provide carboxylate anion for conjugating amino residues ofnucleosides or other drugs.

In general, various techniques may be advantageously employed to improvethe stability characteristics of the polymer conjugates of the presentinvention, including: the functionalization of the polymer with groupsof superior hydrolysis resistance, e.g., the previously illustratedconversion of ester groups to ether groups; modifying thelipophilic/hydrophilic balance of the conjugating polymer, asappropriate to the drug being stabilized by the polymer; and tailoringthe molecular weight of the polymer to the appropriate level for themolecular weight of the drug being stabilized by the polymer.

The unique property of polyalkylene glycol-derived polymers of value fortherapeutic applications of the present invention is generalbiocompatibility. The polymers have various water solubility propertiesand are not toxic. They are non-antigenic, non-immunogenic and do notinterfere with biological activities of enzymes. They have longcirculation in the blood and are easily excreted from living organisms.

The products of the present invention have been found useful insustaining the biological activity of therapeutic nucleosides, peptides,and other therapeutic agents, and may be prepared for therapeuticadministration by microemulsion formulation as hereinafter more fullydescribed. Administration preferably is by either the parenteral or oralroute.

In the dry, lyophilized state, the drug-polymer conjugates of thepresent invention have good storage stability; and solution formulationsof the conjugates of the present invention are likewise characterized bygood storage stability.

The microemulsion formulations of the present invention may be employedfor the prophylaxis or treatment of any condition or disease state forwhich the drug constituent thereof is efficacious.

In addition, the microemulsion formulations of the invention may beemployed for the diagnosis of constituents, conditions, or diseasestates in biological systems or specimens, as well as for diagnosispurposes in non-physiological systems.

Further, the microemulsion formulations of the invention may haveapplication in prophylaxis or treatment of condition(s) or diseasestate(s) in plant systems. By way of example, the active component ofthe formulation may have insecticidal, herbicidal, fungicidal, and/orpesticidal efficacy amenable to usage in various plant systems.

In therapeutic usage, the present invention contemplates a method oftreating an animal subject having or latently susceptible to suchcondition(s) or disease state(s) and in need of such treatment,comprising administering to such animal an effective amount of amicroemulsion formulation of the present invention which istherapeutically effective for said condition or disease state.

Subjects to be treated by the polymer conjugates of the presentinvention include both human and non-human animal (e.g., bird, dog, cat,cow, horse) subjects, and preferably are mammalian subjects, and mostpreferably human subjects.

Depending on the specific condition or disease state to be combated,animal subjects may be administered the microemulsion formulation of theinvention at any suitable therapeutically effective and safe dosage, asmay readily be determined within the skill of the art, and without undueexperimentation.

The microemulsion formulations of the invention may comprise the drugcomponent per se as well as, or alternatively, such drug component inthe form of pharmaceutically acceptable esters, salts, or otherphysiologically functional derivatives thereof.

The present invention also contemplates pharmaceutical formulations,both for veterinary and for human medical use, which comprise as theactive agent one or more therapeutic agent(s).

In such microemulsified pharmaceutical and medicament formulations, theactive agent preferably may be utilized together with one or morepharmaceutically acceptable carrier(s) therefor and optionally any othertherapeutic ingredients. The carrier(s) must be pharmaceuticallyacceptable in the sense of being compatible with the other ingredientsof the formulation and not unduly deleterious to the recipient thereof.The active agent is provided in an amount effective to achieve thedesired pharmacological effect, as described above, and in a quantityappropriate to achieve the desired daily dose.

The formulations include those suitable for parenteral as well asnon-parenteral administration, and specific administration modalitiesinclude oral, rectal, buccal, topical, nasal, ophthalmic, subcutaneous,intramuscular, intravenous, transdermal, intrathecal, intra-articular,intra-arterial, sub-arachnoid, bronchial, lymphatic, vaginal, andintra-uterine administration. Formulations suitable for oral andparenteral administration are preferred.

Formulations of the present invention suitable for oral administrationmay be presented as discrete units such as capsules or other containmentstructures, each containing a predetermined amount of the formulation;or in the emulsified form per se, for ingestion in a predeterminedamount.

A syrup may be made by adding a sugar, for example sucrose, to themicroemulsion, together with any accessory ingredient(s). Such accessoryingredient(s) may include flavorings, suitable preservative, agents toretard crystallization of the sugar, and agents to increase thesolubility of any other ingredient, such as a polyhydroxy alcohol, forexample glycerol or sorbitol.

Formulations suitable for parenteral administration convenientlycomprise the microemulsion in a form which preferably is isotonic withthe blood of the recipient (e.g., physiological saline solution).

The formulations may be presented in unit-dose or multi-dose form.

Nasal spray formulations comprise the purified emulsion withpreservative agents and isotonic agents. Such formulations arepreferably adjusted to a pH and isotonic state compatible with the nasalmucus membranes.

Formulations for rectal administration may be presented as an enemaformulation.

Ophthalmic formulations are prepared by a similar method to the nasalspray, except that the pH and isotonic factors are preferably adjustedto match that of the eye.

Topical formulations may comprise the emulsion in one or more media,such as mineral oil, petroleum, polyhydroxy alcohols, or other basesused for topical pharmaceutical formulations.

In addition to the aforementioned ingredients, the formulations of thisinvention may further include one or more accessory ingredient(s)selected from diluents, buffers, flavoring agents, disintegrants,surface active agents, thickeners, lubricants, preservatives (includingantioxidants), and the like.

In formulations of the present invention, the conjugating polymersdescribed herein may be employed for in vitro stabilization of drugs intherapeutic as well as non-therapeutic applications. The polymers may beemployed for example to increase the thermal stability and enzymicdegradation resistance of the drug. Enhancement of the thermal stabilitycharacteristic of the drug via conjugation in the manner of the presentinvention provides a means of improving shelf life, room temperaturestability, and robustness of research reagents and kits.

The present invention provides pharmaceutically acceptable compositionsin the form of a microemulsion whose HLB value is between 3 and 7. Theformulation may be prepared with surfactant components whose combinedHLB strength in the dosage form is less than 7. The formulation may forexample contain a mixture of surfactants in the lipid phase, and anaqueous phase containing a high HLB surfactant. The presence ofadditional triglycerides, other than the low HLB surfactant, isoptional, but not essential.

The lipid phase of the microemulsion of the invention can containoil-soluble drugs, short chain, medium chain and long chain fatty acidtriglycerides, monoglycerides of fatty acids, diglycerides of fattyacids, and propylene glycol esters of fatty acids, such as propyleneglycol alginate.

The low HLB surfactant of the lipid phase can be any suitablesurfactant. Examples include Sorbitan oleate (Arlacel 80),monoolein/propylene glycol (Arlacel 186), C₈/C₁₀ fatty acid mono- anddiglycerides from coconut oil, soy lecithin, egg phosphatides, citricacid esters of monoglycerides, lactic acid esters of monoglycerides,diacetyl tartaric acid esters of monoglycerides, succinic acid esters ofmonoglycerides, sucrose fatty acid esters, polyglycolyzed glycerides ofoleic acids (e.g., Labrafil M1944), polyglycolyzed glycerides oflineleic acid (e.g., Labrafil M 2125), polyglycerol esters of fattyacids, including both long chain and medium chain fatty acids, e.g.,polyglyceryl decaoleate (such as Caprol PGE 860), and polyglycerylesters of mixed fatty acids such as Caprol ET (polyglyceryl-6 mixedfatty acids).

The hydrophilic phase may contain in addition to water and water-solubledrugs, one or more polyhydroxy compounds such as carbohydrates,polyethylene glycols, and propylene glycol, in any ratio from 0-100% w/wof the aqueous phase. The hydrophilic phase may further containpolyoxyethylene(2) sorbitan oleate (Tween 80), polyoxyethylene(20glycerol trioleate, C₈/C₁₀ polyglycolyzed glycerides from coconut oil(e.g., Labrafac CM 10, and Labrasol), Tween 60, Cremophor EL(ethoxylated castor oil), Cremophor RH 20 (ethoxylated castor oil), andsucrose fatty esters such as sucrose stearate.

The broad range for the amount of high HLB surfactant that can bepresent in the composition can be 0.2%-50% w/w. The preferred range forsuch high HLB surfactant is 0.2-10% w/w. The broad range for the lipidphase containing surfactants is 20-90% w/w. A preferred concentration isaround 70% w/w and the water content of the aqueous phase can be 2-30%w/w with the preferred range being 10-20% w/w. The preferred range ofpolyhydroxy solvents of the hydrophilic phase is 0-20% w/w.

Optional ingredients for the preparation of these emulsions includestabilizers such hydroxy propyl methyl cellulose, hydroxy propylcellulose, carboxymethyl cellulose, and carboxy cellulose, and organicacids such as polyacrylic acids and their partial esters can bebeneficially used in combination.

Other ingredients such as antioxidants and antimicrobial agents can beused in the formulation. The presence of unsaturated fatty acids in thelipid may prone them susceptible to oxidation. Oil soluble butylatedhydroxy anisole, Vitamin-E, and propyl gallate can be used in theformulation in a concentration of 0.1 to 1.2% w/w. Antimicrobialpreservatives, such as parabens and benzalkonium chloride, may also beused to preserve the microemulsion, e.g., in a concentration of 0.1-0.5%w/w.

The microemulsion of the present invention can be prepared by simplymixing by hand or by mild vortexing of the formulation ingradients. Theorder of addition is not crucial, but in cases where the components areviscous the dilution of viscous ingradients with another oil orsurfactant may be helpful. Preparation of protein stock solutionscontaining high concentrations of proteins are convenient to prepare theformulations as compared to dissolving protein powders directly in theemulsion formulation volume. In addition, highly accurate determinationsof protein loading in the emulsion can be made by HPLC trace of thestock solution.

As an illustrative methodology for the preparation of the microemulsionformulations of the invention, an aqueous solution containing lipid andlipid-soluble low HLB surfactant is prepared. The high HLB surfactant ismixed with the lipid phase. Slow addition of appropriate quantities ofthe aqueous solution to the lipid/surfactant mixture results in a cleartransparent solution. Occasional gentle shaking may be desirable duringthe addition. The resulting formulation then can be processed forpackaging and end use. For example, formulations containing less than20% w/w of the hydrophilic phase can be made, and the formulationintroduced to soft gel capsules, such as enteric-coated soft gelcapsules, as unit dosage forms. Alternatively, the formulation can begiven as a liquid in the prescribed or desired dose.

The following Examples are provided to illustrate the present invention,and should not be construed as limiting thereof.

EXAMPLE I

Conjugate 1

Polysorbate trioleate p-nitrophenyl carbonate

To a solution of p-nitrophenylchloroformate (0.8 g, 4 mmole) in 50 mL ofanhydrous acetonitrile is added dry polysorbate trioleate (7 g, 4 mmole)followed by dimethylaminopyridine (0.5 g, 4 mmole). The reaction mixtureis stirred at room temperature for 24 hours Solvent is removed underreduced pressure and the resultant precipitate is diluted with drybenzene and filtered through Celite. The residue is refrigeratedovernight in dry benzene and the additional precipitate is removed byfiltration. Solvent is removed under reduced pressure and residualbenzene is removed by evacuation at low pressure to yield 6.4 g ofpolysorbate trioleate p-nitrophenyl carbonate.

Coupling of insulin with activated polymer

To a solution of activated polysorbate trioleate (1 g) in aqueousmixture of dimethylsulfoxide (DMSO) or dimethylformamide (DMF) is addeda solution of bovine insulin (50 mg) in 0.1 M pH 8.8 phosphate buffer.pH is maintained by addition of 1N NaOH as necessary. The reactionmixture is stirred at room temperature for 2.5 h. After this time themixture is subjected to gel filtration chromatography using SephadexG-75. Purification by elution with 0.1M pH 7.0 phosphate buffer andcollection of fractions with an automated fraction collector yieldsConjugate 1. The polymer content is determined bytrinitrobenzenesulfonic acid (TNBS) assay and mass spectrometry, and theprotein concentration by Biuret Method. A molar ratio of polymer toinsulin is determined to be 1:1. Conjugate I is also obtained by usingpure organic solvent (e.g., DMSO, DMF).

EXAMPLE II

Conjugate 2

The terminal hydroxyl group of polyethylene glycol monostearate isactivated by reaction with p-nitrophenyl chloroformate as describedabove. To a solution of the activated polymer (1 g) in distilled wateris added bovine insulin (80 mg) dissolved in 0.1M phosphate buffer, atpH 8.8. The pH is maintained by careful adjustment with 1N NaOH. Afterstirring for 3 hours, the reaction mixture is quenched with excessglycine and subjected to gel filtration chromatography using SephadexG-75. Insulin/polymer conjugate is collected and lyophilized. Proteincontent is determined by Biuret assay, giving a quantitative yield.

EXAMPLE III

Conjugate 3

Tetrahydro-2-(12-bromododecanoxy)-2H pyran

To a solution of 12-bromo-1-dodecanol (1 mole) in dichloromethanecontaining pyridinium p-toluenesulfonate (P-TSA) is added dihydropyran(2 moles). The reaction mixture is stirred for 24 hours and then washedtwice with water and dried over anhydrous MgSO₄. The dichloromethane isremoved under reduced pressure. If necessary the resulting product ispurified by chromatography on silica gel.

Coupling of polyethylene glycol to the terahydropyran derivative

The tetrahydropyran derivative described above, dissolved in drybenzene, is added to a solution of polyethylene glycol (1 mole) in drybenzene containing NaH (1 mole). The reaction mixture is stirred at roomtemperature for 24 hours. After that time the mixture is eluted througha silica gel column with benzene. Additional purification by columnchromatography, if necessary, is performed. The protectivetetrahydropyran group is removed by treatment with p-TSA at roomtemperature. The final product is purified, if necessary, by columnchromatography. The hydroxyl group of the polymer is activated byreaction with p-nitrophenylchloroformate as described hereinabove.Conjugation with insulin is carried out as described for Conjugate 1.

EXAMPLE IV

Comparative studies using bovine insulin were conducted onpolymer-insulin conjugates and on native insulin to determine theirrelative stability and activity in animal models. In the animal studies,the efficacy of the polymer-insulin in lowering the blood level wascompared to that of native insulin. Female and male albino miceaveraging 25 g in weight were fasted overnight and used in groups offive for each treatment conducted in several phases over a period of twodays.

Each test animal received a single dose of either native insulin (Group1, 100 μg/kg, subcutaneously); native insulin (Group 2, 1.5 mg/kg,orally by gavage); Conjugate 1) Group 3, 100 μg/kg, orally); orConjugate 1 (Group 4, 100 μg/kg, subcutaneously) at time 0. Anadditional group (Group 5) received no insulin of any kind but waschallenged with glucose 30 minutes before scheduled sampling times.Animals were fasted overnight before treatment and for the duration ofthe study. All test materials were prepared in phosphate bufferedsaline, pH 7.4. Thirty minutes before scheduled sampling times of 0.5,1, 2, 4, 8 and 24 hours following treatment with insulin, animals werechallenged with a bolus dose of glucose (5 g/kg, as a 50% solution,given orally), so that each animal received only one dose of insulin orConjugate 1 and one glucose challenge. At the scheduled sample timeblood was collected from the tail vein and immediately analyzed forglucose content using a One Touch Digital Glucose Meter (Life Scan). Theresults of the test are shown in FIG. 1, for Groups 1-5.

Blood glucose levels for Group 1 animals (native insulin, subcutaneous)were approximately 30% of control (Group 5, untreated) animals at the 30minute time point. This hypoglycemic effect lasted only 3.5 hours inGroup 1 animals. Native insulin administered orally (Group 2) loweredblood glucose levels to a maximum of 60% of control, this maximumresponse occurring 30 minutes after treatment with the insulin. Incontrast the glucose levels in animals in Group 3 (Conjugate 1, 100μg/kg, p.o.) were lowered with an apparent delayed onset of hypoglycemicactivity. The hypoglycemic activity in Group 3 animals was greater thanthat in Group 2 animals even though the dose of insulin administered toGroup 3 was only one fifteenth of that given to Group 2. At all timepoints after 3 hours glucose levels were lower for Group 3 animals thanfor any other treatment group, the largest difference being at the fourto eight hour sampling points. Glucose levels in Group 4 animals(Conjugate 1, 100 μg/kg, s.c.) followed the same course as those forGroup 1 animals for the first four hours of the study. After four hoursGroup 2 glucose levels remained above control (untreated, Group 5)levels whereas Group 4 glucose levels dropped, at eight hours, to 62% ofGroup 5 levels, and remained below Group 5 levels.

EXAMPLE V

An insulin efficacy study was conducted on male and female albino miceusing as test materials insulin in unconjugated form, and Conjugate 1.One objective of this study was to determine whether insulin in the formof Conjugate 1 is capable of acting on blood glucose levels in the sameway as insulin when administered subcutaneously. A second objective wasto determine whether the insulin complex of Conjugate 1, unlike freeinsulin, is capable of acting to decrease the blood glucose level whenadministered orally. The results are shown in FIG. 2, wherein “InsulinComplex” denotes Conjugate 1.

Baseline blood samples were obtained for serum glucose analysis from 10fasted untreated albino mice (5 males and 5 females); baseline values inFIG. 2 are denoted by the symbol “O”. Three additional groups (fivemales and five females each) were fasted overnight and loaded withglucose alone orally by gavage (5 g/kg body weight). Ten animals weresacrificed at each of three time periods to obtain blood samples forglucose analysis: 30, 60 and 120 minutes after dosing. A commercialinsulin and Conjugate 1 were each administered both orally (p.o) andparenterally (s.c.) to groups of fasted mice (five males and fivefemales, for sacrifice and blood analysis at each of the three timeperiods), to provide different treatment regimens. The treatment,administration routes, and symbols shown for results in FIG. 2 included:(i) glucose (5 g/kg p.o.), symbol: “”; (ii) insulin (100 μg/kg, s.c.)and glucose (5 g/kg p.o.), symbol: “—”; (iii) insulin (1.5 mg/kg, p.o.)and glucose (5 g/kg p.o.), symbol: “—”; (iv) Conjugate 1 (100 μg/kg,s.c.) and glucose (5 g/kg p.o.), symbol “ ”; (v) Conjugate 1 (250 μg/kg,s.c.) and glucose (5 g/kg p.o.), symbol: “▪”; (vi) Conjugate 1 (1.5mg/kg, s.c.) and glucose (5 g/kg p.o.), symbol: “Δ”. In these tests ofConjugate 1, the concentration of the protein in the administeredsolution was 0.1 mg protein/mL solution; for comparison purposes, amodified covalently bonded insulin-polymer conjugate, having a proteinconcentration in the administered solution of 0.78 mg protein/mLsolution, was included, (vii) modified Conjugate 1 (100 μg/kg, s.c.) andglucose (5 g/kg p.o.), symbol: “Δ”.

The insulin was administered 15 minutes prior to glucose loading.

Glucose was administered orally by gavage to all but the baseline groupof animals at a dose of 5 g/kg (10 mg/kg of a 50% w/v solution in normalsaline). When insulin was administered orally by gavage, it was given ata dose of 1.5 mg/kg (18.85 mL/kg of a 0.008% w/v solution in normalsaline). When insulin was administered subcutaneously, it was given at adose of 100 μg/kg (2.5 mL/kg of a 0.004% w/v solution in normal saline).When the Conjugate 1 polymer-insulin complex was administered orally bygavage, it was given at a dose of 1.56 mg/kg (2.0 mL/kg of the undilutedtest material). When the Conjugate 1 polymer-insulin complex wasadministered subcutaneously, it was given at a dose of 100 μg/kg (1.28mL/kg of a 1:10 dilution of the 0.78 mg/mL solution received) or 250μg/kg (3.20 mL/kg of a 1:10 dilution of the solution received). Themodified Conjugate 1 contained 0.1 mL insulin/mL and was dosed at a rateof 1.0 mL/kg to obtain a 100 μg/kg dose.

Glucose was measured using the Gemini Centrifugal Analyzer and purchasedglucose reagent kits. The assay was a coupled enzymatic assay based onthe reaction of glucose and ATP catalyzed by hexokinase, coupled withthe glucose-6-phosphate dehydrogenase reaction, yielding NADH. Duplicatesamples were analyzed and the mean value reported. Dilution (1:2 or 1:4)of some serum samples was necessary in order to determine the very highglucose concentration present in certain samples.

After glucose loading, mean serum glucose rose to a high level at 30minutes, declined at 60 minutes, and was below baseline at 120 minutes.If commercial insulin was administered subcutaneously (100μg/kg bodyweight, it was highly effective in preventing the increase in bloodglucose. However, if insulin was given orally (at a high dose of 1.5mg/kg) there was no effect on the rise of blood glucose. This wasexpected, since insulin, a protein, is readily hydrolyzed in thedigestive tract and is not absorbed intact into the bloodstream.

When Conjugate 1 was given subcutaneously at either 100 or 250 μg/kgdosage, it was highly effective in restricting the rise in blood glucoseafter glucose loading. Mean serum glucose values were significantlylower after the 100 μg/kg dose of Conjugate 1 at both 30 and 60 minutesthan they were after 100 μg/kg of free insulin. Mean serum glucose at250 μg/kg of Conjugate 1 was lower, though not significantly, at 30minutes, significantly lower at 60 minutes and at 120 minutes wasreturned to the baseline. With both free insulin at 100 μg/kg andConjugate 1 at 100 μg/kg, the glucose level remained below baseline at120 minutes.

The modified Conjugate 1 administered at 100 μg/kg produced asignificant reduction in blood glucose at 30 minutes.

EXAMPLE VI

Preparation of Para-Nitrophenyl Carbonate of Polysorbate Monopalmitate

Polysorbate monopalmitate is first dried by the azeotropic method usingdry benzene.

To a solution of the dry polymer (2 g, 2 mmole) in 10 mL of dry pyridineis added para-nitrophenylchloroformate (0.6 g, 3 mmol). The mixture isstirred at room temperature for 24 hours. The reaction mixture ischilled in ice and diluted with dry benzene and filtered through filteraid. This procedure is repeated and finally the solvent is removed atthe rotary evaporator. Traces of solvent are removed in vacuo. The yieldof the product is 1.8 g.

EXAMPLE VII

Preparation of Polysorbate Monopalmitate Conjugate with Insulin

In accordance with the previously described conjugation reactionprocedure of Example I but using polysorbate monopalmitate in the amountof 1 g and insulin in the amount of 80 mg, with HPLC separation of thereaction product, an insulin-polysorbate monopalmitate covalently bondedconjugate is obtained.

EXAMPLE VIII

Preparation of Enzyme-polymer Conjugates

Coupling of alkaline phosphatase (AP) to polymer was carried out usingthe same procedure as described for Conjugate 1 in Example I. Inaddition, to determine whether a high or low ratio of polymer to proteinwould be more advantageous, conjugates were prepared using 140 moles ofpolymer/mole of enzyme and 14 moles of polymer/mole of enzyme. Thenumber of polymer groups per molecule of conjugated AP are 30 and 5,respectively, for the high and low ratios of polymer.

The following procedure was employed to obtain about 5 groups/moleculeof alkaline phosphatase: 4.1 mg (salt free) was dissolved in 0.05M.sodium bicarbonate. To this solution was added activated polymer (0.75mg) in water/dimethyl-sulfoxide and the solution was stirred for 3 to 12hours at room temperature. The resulting reaction mixture was dialyzedagainst a salt solution (0.3N NaCl) in dialysis tubing (MW cutoff12,000-14,000) over 12 hours with 4 to 6 changes of dialysis solution.The same procedure was used for the high ratio. Total proteinconcentration of dialyzed material was determined by Biuret method.

Activity Measurement and Stability Study

The phophatase assay was performed according to the method of A. Volleret al, Bulletin WHO, 53, 55 (1976). An aliquot (50 microliter) was addedto microwells and mixed with 200 microliter of substrate solution (10g/L, 4-nitrophenylphosphate in 20% ethanolamine buffer, pH 9.3) andincubated at room temperature for 45 minutes. The reaction was stoppedby 50 microliter of 3M NaOH. The absorbence was measured at 405 nm in amicro plate reader.

Phosphatase activity was compared with that of native enzyme undervarious conditions.

Dilute solutions containing similar concentrations of alkalinephosphatase and alkaline phosphatase-polymer conjugates were stored atvarious temperatures. The enzymatic activity was tested periodically.The two polymers tested at 5° C., 15° C., 35° C. and 55° C. werecompared to the control alkaline phosphatase stored at 5° C.

As can be seen from Table A, the initial enzymatic activity of bothpolymers was about three-fold higher than the control. Bothpolymer-enzyme conjugates had enhanced thermal stability over the nativeenzyme. This is especially evident for the conjugate characterized bythe higher ratio of polymer to enzyme.

TABLE A DAY TEMP, ° C. O 2 3 4 5 6 AP/HIGH  5 399 360 321 371 343 337 15158 115 126 24 184 35 132 112 135 138 123 55 36 25 10 14 AP/LOW  5 324252 210 220 162 159 15 83 47 40 38 51 35 61 36 35 33 32 55 17 6 2 2AP/CONTROL  5 100 100 100 100 100 100 15 89 74 43 36 28 35 53 48 21 2020 55 10 2 1 2

EXAMPLE IX

Conjugate 1A

To a solution of insulin (50 mg) in 0.05 M sodium bicarbonate buffer ofpH 9.2 is added a solution of activated polymer (1 g) inwater/dimethylsulfoxide and stirred for 3 hours, at room temperature.The pH of the mixture is maintained by careful adjustment with 1N NaOH.The reaction mixture then is dialyzed against 0.1M pH 7.0 phosphatebuffer. Purified product is lyophilized. Protein content (48 mg) isdetermined by Biuret assay. The number of polymer chains linked toinsulin is determined by TNBS assay, giving a ratio of two moles ofpolymer to one mole of insulin.

EXAMPLE X

Synthesis Of OT_(10C)AraCMP

Synthesis of tributylAraCMP

A mixture of 200 mg of AraCMP (0.62 mmole), 1 mL of pyridine, 161 μl oftri-n-butylamine (0.67 mmole) and 1.1 mL of anhydrous butyric-anhydride(6.2 mmole) was stirred for 21 hours at room temperature. Methanol (1ml) was added to the reaction mixture to destroy unreacted butyricanhydride and stirred for 1 hour. The reaction mixture was then stirredwith water (0.5 ml) for 24 hours at room temperature to cleave thebutyric phosphate bond. After roto-evaporating the solvent, the product,tributylAraCMP was extracted into 10 ml of chloroform and the organiclayer was washed with 3×15 ml of water. The chloroform layer was driedover MgSO₄ and evaporated to dryness. This product was used in the nextstep without further purification.

Conjugation of OT₁₀C (polyoxyethylene [10]cetylether) to tributylAraCMP

TPSCI (1.3 mmole) was dissolved in 6 ml of anhydrous chloroform andadded to tributylAraCMP and stirred for 40 minutes at room temperature.The resulting TPS activated tributylAraCMP was added to 876 mg of OT₁₀(1.2 mmole) in 2.1 mL of pyridine and stirred at room temperature for 4½hours. TLC of the reaction mixture in THF: methanol (10:0.75 v/v) showedcomplete disappearance of tributylated AraCMP. The solvent wasevaporated and the product was suspended in 6 ml water and extractedinto 2×6 ml of chloroform.

The butyl groups of the OT₁₀ conjugated AraCMP were deprotected bystirring the chloroform layer with 4.5 ml of 2.0M ammonia solution inethanol overnight at room temperature.

Purification of OT₁₀Conjugated AraCMP

Solvent was rotoevaporated from the reaction mixture above and TPSsulfonic acid was precipitated with 15 ml water. The pH of the aqueouslayer was reduced to 1-2 and the product was extracted into 6×35 ml ofchloroform. HPLC of the chloroform layer on an analytical C8 column inisopropanol-water-0.1% TFA showed a hydrophobic nucleoside product.³¹PNMR of the product shows attachment of a polymeric residue to thephosphate moiety and ¹H NMR shows the polymeric as well as thenucleoside resonances. The product was purified on C-8 column withisopropanol-water 0.1% TFA gradient.

EXAMPLE XI

A microemulsion formulation according to the invention was prepared withthe composition shown below.

Quantity, % Component Added HLB Value HLB Contribution CAPMUL MCM ™ 53.05.5 4.86 CENTROPHASE 31 ™ 5.7 3.4 0.38 Propylene glycol 19.9 Tween 801.4 15.0 0.35 Hexyl insulin in 15 mg/mL NaP buffer q.s Total 100 5.59

The propylene glycol content of the above emulsion can be lowered byreducing combined HLB strength of the emulsion. At the same time, thedrug loading in the formulation can be increased, as shown in thefollowing Example.

EXAMPLE XII

A microemulsion formulation was prepared with the composition identifiedin the following table:

Quantity, % Component Added HLB Value HLB Contribution LABRAFIL M 1994 ™19.2 3.5 0.855 CAPMUL MCM ™ 46.1 5.5 3.23 CENTROPHASE 31 ™ 11.0 3.40.489 Propylene glycol 1.9 Tween 80 2.3 15.0 0.64 Hexyl insulin in NaPq.s., 30 mg buffer protein in buffer Total 100 5.0

The aqueous phase of the above microemulsion can have polyhydroxylicalcohols such as manitol, which will reduce the amount of propyleneglycol and the high HLB surfactant essential to form a similar water inoil (w/o) microemulsion.

EXAMPLE XIII

A microemulsion formulation according to the invention was prepared withthe composition shown below.

Quantity, % Component Added HLB Value HLB Contribution CAPUL MCM ™ 45.35.5 4.72 CENTROPHASE 31 ™ 6.4 3.4 0.48 Propylene Glycol 14.5 Tween 801.0 15.0 0.29 Mannitol 16.8 mg/mL of final formulation Hexyl insulin inNaP q.s., (16.6 buffer mg protein/mL of final emulsion) Total 100 5.49

Alternatively, the aqueous phase of this type microemulsion canaccommodate a mixture of polyethylene glycol 300 and polyethylene glycol400 in addition to propylene glycol in the aqueous phase. as in thefollowing formulation of Example XIV.

EXAMPLE XIV

A microemulsion formulation according to the invention was prepared withthe composition shown below.

Quantity, % Component Added HLB Value HLB Contribution CAPMUL MCM ™ 54.15.5 4.80 CENTROPHASE 31 ™ 6.45 3.4 0.42 Propylene glycol 14.5 Tween 801.5 15.0 0.36 Polyethylene glycol 400 4.9 Polyethylene glycol 300 3.9Hexyl insulin in NaP q.s., (18.8 buffer mg protein/mL of final emulsion)Total 100 5.58

Alternatively, an alcohol free w/o microemulsion of similar combined HBLstrength can be formed using propylene glycol mono and diesters ofmedium chain fatty acids (Captex 200) and sodium octanoate (anionicsurfactant). The high protein load in the microemulsion formulation isan added advantage, as shown in the following Example XV.

EXAMPLE XV

A microemulsion formulation according to the invention was prepared withthe composition shown below.

Quantity, % Component Added HLB Value HLB Contribution CAPMUL MCM ™ 20.05.5 3.12 CENTROPHASE 31 ™ 13.3 3.4 1.51 CAPTEX 200 ™ 40.0 SodiumOctanoate 1.86 20-23.0 1.22 Hexyl insulin in NaP q.s., (46.6 buffer mgprotein/mL of final emulsion) Total 100 5.85

The formulation of similar HLB strength microemulsions containing highprotein load can be obtained without the use of anionic surfactant orethoxylated nonionic surfactant. For example decaglycerol mono anddioleate (CAPROL 860™), a high HLB surfactant (HLB=11) can be used alongwith CAPMUL MCM™ and lecithin to form a microemulsion containing highprotein load, as in the following Example XVI.

EXAMPLE XVI

A microemulsion formulation according to the invention was prepared withthe composition shown below.

Quantity, % Component Added HLB Value HLB Contribution CAPMUL MCM ™ 63.05.5 4.4 CENTROPHASE 31 ™ 12.1 3.4 0.61 CAPROL 860 ™ 4.1 11 0.57 Hexylinsulin in NaP q.s., (40 mg buffer protein/mL of final emulsion) Total100 5.58

By suitable choice of excipients which are solids at room temperature, asolid or semi-solid microemulsion can be prepared. For example WhitepsolH15 (solid C₈/C₁₀ triglyceride), Imwitor 308 (C₁₀ mono anddiglycerides), Egg lecithin (solid at RT) and Gelucire 44/14, a soliddosage form of desired HLB can be obtained.

The liquid microemulsions of the above examples can be encapsulated in asuitable solid hard fat and delivered in a capsule as a unit dosageform. The capsules can be enteric-coated and targeted for absorption inthe intestine. Alternatively, the liquid emulsions can be filled in asoft gel capsule and delivered for absorption in the intestine. Thesesoft gel capsules can also be enteric-coated for absorption in specificareas of the intestine.

Alternatively, the protein or other therapeutic agent can be dispersedin a mixture of lipid and surfactant in accordance with the presentinvention and filled in a soft gel capsule as a pre-emulsionconcentrate. These concentrates can self-emulsify under biologicalenvironment exposure conditions to form the desired final emulsion.

EXAMPLE XVII

Synthesis of Hexyl polymer and Hex-Insulin conjugate

A. Preparation of Methyl(ethyleneglycol)₇-O-ethyl hexanoate

A solution of methyl(ethyleneglycol)₇-OH (25 g: 7142 mmol) in drytetrahydrofuran (THF) (52 mL) was added dropwise to a stirred suspensionof NaH (3.057 g: 76.4 mmol, of 60% oil dispersion) in dry THF (71 mL).During the addition, the reaction temperature was kept below 20° C.After addition, the resulting solution was allowed to stir for 3 h. Atthe end of this period, 1-bromo ethyl hexanoate (15.93 g: 71.4 mmol),dissolved in dry THF (20 mL) was added dropwise, and the mixture wascontinued to stir for 6-8 hours. The solvent was removed under reducedpressure and the residue was treated with cold water (100 mL), andextracted with ethyl acetate (3×30 mL). The combined organic layer waswashed sequentially with water (1×20 mL), brine (1×20 mL), dried overMgSO4 and the solvent was evaporated at reduced pressure to givemethyl(ethyleneglycol)₇-O-ethyl hexanoate as a pale yellow oil. The oilwas chromatographed on silica gel column and eluted firstly with ethylacetate-hexane (1:1) which removed mineral oil and bromo ethylhexanoatealong with other smaller fractions of polymer. Later elution withdicholoromethane-methanol (80:20) yielded puremethyl(ethyleneglycol)₇-O-ethyl hexanoate.

B. Preparation of Methyl(ethyleneglycol)₇-O-hexanoic Acid

The ester (25 g; 50.813 mmol) was stirred with 1N NaOH (76.21 mL) atroom temperature for 3 h. The aqueous layer was cooled to 0° C. byadding ice and acidified with 6N HCl to pH 2-3 and extracted withdichloromethane (3×25 mL). The combined organic layer was washed withwater (1×20mL), brine (1×20 mL), dried over MgSO4, filtered andevaporated to leave an oil. The product was purified by columnchromatography on silica gel. Elution with pure ethyl acetate removedthe impurity. Further elution with dichloromethane-methanol (80:20) gavepure methyl(ethylenaglycol)₇-O-hexanoic acid.

C. Activation: Preparation of Methyl(ethyleneglycol)₇-O-hexanoicAcid-N-hydroxy-succinimide ester

To a stirring solution of methyl(ethyleneglycol)₇-O-hexanoic acid (25 g:53.87 mmol) in dry methylene chloride (134.69 mL) under nitrogenatmosphere, solid N-hydroxysuccinimide (6.20 g; 53.87 mmol) was added.The stirring solution, solid EDC (11.36 g; 59.26 mmol) were added inportion and the solution was stirred at room temperature for 4 h. At theend of this period the solution was treated with water (2×20mL), 1N HCl(1×20mL), water (1×20 mL), 1N sodium bicarbonate (2×20 mL), water (1×20mL), 1N HCl (1×20 mL), water (1×20 mL), and brine. The organic layer wasdried over MgSO₄, filtered and evaporated under reduced pressure at roomtemperature to give pure activated ester.

D. Conjugation of Methyl(ethyleneglycol)₇-O-hexanoic acid NHS to insulin

Insulin was dissolved in dimethyl sulfoxide at 25° C. and reacted with1.2 molar equivalent of activated methyl(ethyleneglycol)₇-O-hexanoicacid for 45 minutes at 25° C. The product mixture (see Table B)containing monoconjugate (42±2.5%, aveg. M.W 6200), diconjugate(39±2.5%, Ave. M.W 6334), triconjugate (4±2.5%, Avge. M.W 7074) andunreacted insulin (12.5±2.5%, Avge. M.W 5734) was purified by dialysison a 3500 MW cut off membrane at 5° C. The solution was lyophilized andprotein content, product distribution and purity was determined byreverse phase HPLC. The molecular weights of products were determined byMALDI(TOF)/MS. The product mixture was analyzed for moisture, aceticacid and traces of bromo impurity.

Composition of Hex-Insulin Mixture

The hex-insulin mixture contains mainly mono and disubstituted insulinconjugates. Triconjugate and free insulin are present as the minorcomponents. The specification of the components present in the productis given in Table B below and the stability characteristics of thehex-insulin mixture are shown in Table C below, in comparison withnative insulin.

TABLE B Specification for HEX-Ins Mixture Composition: FractionComposition Free insulin 12.5 ± 2.5% monoconjugate (pK1) 42.0 ± 2.5%diconjugate (pK2) 39.0 ± 2.5% triconjugate (pK3)  4.0 ± 2.5%

TABLE C Stability Studies of HEX-Insulin (Bovine) and Native InsulinCondition Insulin (Na) HEX-Insulin Mix 1. Acid^(a) 153 hrs. stable > 153hrs. 2. Pepsin (Gastric)^(b) 9 min. 107 min. 1.5 units/mL 3.Pancreatin^(c) 77 min. 126 min 6 units/mL 4. Chymotrypsin^(d) l3 min. 39min. 5. Aggregation^(e) 2-3 days >14 days Stability study experimentalconditions and reference: ^(a)USP 23, 1995 page 2053; Simulated gastricacid, pH 1.3, temp, 37° C. ^(b)USP 23, 1995 page 2053; Gastric juicewith pepsin, pH 1.3, temp. 37° C. ^(c)USP 23, 1995 page 1149, 2053;Pancreatin (Intestinal fluid simulated), pH 7.5, temp. 37° C. ^(d)K.Mitra et al., Pharm. Research, Vol. 10, No. 11, 1993, page 1638; pH 6.0temp. 37° C. ^(e)R. Langer et al., Pharm. Research, Vol. 11, No. 1,1994, page 21; protein conc. 1.0 mg/mL, pH 7.4 (0.01M), temp. 37° C.

EXAMPLE XVIII

FIG. 3 is a graph of ELISA assay results for native insulin in the NRSpool of various Sprague-Dawley rats, showing insulin concentration as afunction of time, prior to and after dosing with insulin, at respectivedoses of 10 milligrams of insulin per kilogram of body weight, and at 30milligrams of insulin per kilogram of body weight. Two rats were dosedat 10 milligrams insulin per kilogram of body weight (Rats C and I) andtwo rats were dosed at 30 milligrams insulin per kilogram of body weight(Rats K and L). The data show that the baseline level of the NRS pool isabout 3.5 nanograms of insulin per milliliter.

FIG. 4 is a graph of ELISA assay results for insulin in the NRS pool ofvarious Sprague-Dawley rats, showing insulin concentration as a functionof time, prior to and after dosing with insulin, at respective doses of10 milligrams of insulin per kilogram of body weight, and at 30milligrams of insulin per kilogram of body weight, wherein the insulinis administered as a conjugate, insulin-hexyl-PEG₇-OMe.

FIG. 5 is a graph of percent of pre-dose blood glucose level as afunction of time, for free insulin, and for conjugated insulin atrespective doses of 1, 3 and 10 milligrams of insulin per kilogram ofbody weight, against a control of phosphate buffered solution (PBS) andbovine serum albumen (BSA).

The foregoing data show that the native insulin concentration in the NRSpool is flat throughout the timecourse, while the conjugate has a highdose peak in 30 minutes with 40 ng/mL insulin.

There is a rise in insulin in the intermediate dose but the peak fallsbelow the level of the NRS pool.

The data therefore show that the conjugate exhibits very good activityin the CLA and this corresponds with an increase in serum insulin to 40ng/mL that peaks in 30 minutes.

EXAMPLE XIX

FIG. 6 is a graph of insulin and blood glucose levels as a function oftime, after dosing of canine subjects with a microemulsion insulinformulation representative of the present invention. The respectivecurves shown in the graph include native Zinc insulin; glucose ( ),hex-insulin; glucose (▪); native Zinc insulin; insulin (Δ); andhex-insulin; insulin (Δ).

These data each represent the average of several determinationsperformed on two pairs of dogs on two separate days.

Glucose data were normalized to the baseline glucose levels (0 minutes).Dogs were dosed orally with one of two emulsion formulations (nativeZinc insulin or Hex-insulin mixture). The dose was adjusted to 1.0mg/kg. Samples were collected at 30 minute intervals. The data werecorrected for Hex-insulin reactivity in the BMI ELISA and Pharmacia RIAtests.

As shown in FIG. 6, dogs dosed with Hex-Ins showed a slightly greaterglucose depression than dogs dosed with native insulin. Maximal glucosedepression was from 9-180 minutes, with a return to baseline by 360-480minutes. In contrast, the insulin levels in the Hex-Ins group were about4 fold higher than the native insulin group. Peak activity of insulinimmunoreactivity in the serum occurred within 30 minutes of dosing, andreturned to baseline in all cases with 120-240 minutes.

While the invention has been described herein, with certain features,and embodiments it will be recognized that the invention may be widelyvaried, and that numerous other modifications, variations, and otherembodiments are possible, and such modifications, variations, and otherembodiments are to be regarded as being within the spirit and scope ofthe invention.

Throughout this specification reference is made to various tradenamesknown in the art. The composition of the various substances referred toas tradenames are set forth in the Table D.

TABLE D Tradename/Class/Source Composition/Properties/ReferenceTradename: Capmul MCM Composition Identification: monodglycreides andClass: monodglyreides and diglycerides of medium chain fatty acidsdiglycerides of medium chain Composition Properties: fatty acids(capryllic and Form: liquid/semi-solid capric) Color, Lovibond Red: 4.0max Source: Abitec Corporation, Acid Value: 2.5 max Columbus, OHMoisture, Karl Fischer: 0.5% max α-monocaprylate: 55% min α-mono-oleate:80% min Free Glycerol: 2.5% max Iodine Value: 2.0 max Residue onIgnition: 0.5% Heavy Metals: 10 ppm Specific Gravity: 0.97-1.02Viscocity, cSt: 40-55 Reference: Data Sheet from Manufacturer Tradename:Caprol 860 Composition Identification: decaglycerol monodioleate Class:polyglycerol esters Composition Properties: Source: Abitec Corporation,Acid Value: 6 max Columbus, OH Color, Gardner: 10 max SaponificationValue: 90-105 HLB: 11.0 Iodine Value: 60 max Reference: Data Sheet fromManufacturer Tradename: Captex 200 Composition Identification: propyleneglycol Class: propylene glycol esters dicaprylate/dicaprate Source:Abitec Corporation, Composition Properties: Columbus, OH Acid Value: 0.1max Color, APHA: 100 max Saponification Value: 315-335 Iodine Value: 1.0max Moisture, KF: 0.1% max Form: clear liquid Viscocity (25° C.):0.92-0.96 Cloud Point: ≦−15° C. Reference: Data Sheet from ManufacturerTradename: Centrophase 31 Composition Identification: lecithin Class:lectithin Composition Properties: Source: Central Soya Co., Inc.,Acetone Insolubles (%): 60-64 Fort Wayne, IN Acid Value (mg/KOH/g):28-35 Color, Gardner: 17 max Hexane Insolubles (%): 0.01 max Moisture(%) 0.8 max Viscocity (cP at 25° C.): 8,500 max Reference: Data Sheetfrom Manufacturer Tradename: Labrafil M 1944 CompositionIndentification: unsaturated polyglycolized glycerides obtained bypartial hydrolysis of kernel oil Class: trans-esterification (apricot),consisting of glycerides and polyethylene glycol product of naturalvegetable oil esters triglycerides and polyalkylene CompositionProperties: Source: Gattefosse, St Priest, HLB: 4 France Appearance:liquid at 40° C. Color, Gardner: <5 Specific Gravity at 20° C.:0.935-0.955 Refractive Indes at 20° C.: 1.465-1.475 Viscocity at 20° C.(mPa.s): 75-95 Acid Value (mg/KOH/g): <2.00 Saponification Value(mg/KOH/g): 155-169 Iodine Vlaue (g 12/100 g): 79-89 Hydroxyl Value (mgKOH/g): 45-65 Peroxide Value (meq O2/kg): <12.5 pH (at 10% in H2O):4.5-6.0 Alkaline Impurities (ppm NaOH): <80 Water Content (%): <0.50Free Glycerol Content (%): <3.0 1 Monoglyceride Content (%): <9.0Sulphated Ashes (%): <0.10 Heavy Metals (ppm Pb): <10 Solubilities at20° C. Ethanol 96° C.: insoluble CHCl3, CH2Cl2: soluble Water:dispersable Vegetable Oil: soluble Mineral Oil: very soluble Reference:Data Sheet from Manufacturer

What is claimed is:
 1. A composition for presentation or delivery of aninsulin-methyl(ethyleneglycol)₇-O-hexanoic acid conjugate, saidcomposition: (a) comprising a water-in-oil (w/o) microemulsionincluding: (i) a lipophilic component; and (ii) a hydrophilic component;and (iii) a therapeutically effective amount of insulin conjugated to 1,2, and/or 3 methyl(ethyleneglycol)₇-O-hexanoic acid conjugates; and (b)having an HLB value between 3 and
 7. 2. A composition according to claim1, wherein the HLB value is from about 5 to about 6.5.
 3. A compositionaccording to claim 1, wherein the HLB value is from about 5 to about 6.4. A composition according to claim 1, wherein the HLB value is between5 and
 6. 5. A composition according to claim 1, wherein the lipophilicphase constitutes from about 30 to about 90 percent by weight of thecomposition.
 6. A composition according to claim 1, wherein thelipophilic phase comprises mono, di, and triglycerides of medium chainor long chain fatty acids.
 7. A composition according to claim 1,wherein the hydrophilic phase comprises a surfactant with an HLB valuegreater than
 8. 8. A composition according to claim 7, wherein thesurfactant comprises a non-ionic surfactant.
 9. A composition accordingto claim 1, wherein the hydrophilic phase comprises a mixture ofpolyhydroxy alcohols selected from the group consisting of polyethyleneglycol, propylene glycol and mannitol.
 10. A composition according toclaim 1, of a pharmaceutically acceptable character.
 11. A compositionfor presentation or delivery of aninsulin-methyl(ethyleneglycol)₇-O-hexanoic acid conjugate, saidcomposition: (a) comprising a water-in-oil (w/o) microemulsioncomprising: (i) a lipophilic component selected from the groupconsisting of monoglycerides and diglycerides of medium chain fattyacids; (ii) a hydrophilic component comprising propylene glycol; (iii) asurfactant component comprising lecithin and tween 80; and (iv) atherapeutically effective amount of insulin conjugated to 1, 2, and/or 3methyl(ethyleneglycol)₇-O-hexanoic acid conjugates in an aqueoussolution; and (b) having an HLB value between 3 and
 7. 12. Themicroemulsion formulation of claim 11 wherein the HLB value is from 5 to6.5.
 13. The microemulsion formulation of claim 11 wherein the HLB valueis from 5 to
 6. 14. The microemulsion formulation of claim 11 whereinthe HLB value is between 5 and
 6. 15. The microemulsion formulation ofclaim 11 wherein the HLB value is 5.59.
 16. The microemulsionformulation of claim 11 wherein the HLB value is 5.6.
 17. Themicroemulsion formulation of claim 11 wherein the aqueous solution is anNaP buffer.
 18. The microemulsion formulation of claim 11 with theproviso that the formulation does not comprise a protease inhibitor. 19.A composition for presentation or delivery of aninsulin-methyl(ethyleneglycol)₇-O-hexanoic acid conjugate, saidcomposition: (a) comprising a water-in-oil (w/o) microemulsionincluding: (i) one or more lipophilic components selected from the groupconsisting of monoglycerides and diglycerides of medium chain fattyacids, and trans-esterification products of natural vegetable oiltriglycerides and polyalkylene polyols; (ii) a hydrophilic componentcomprising propylene glycol; (iii) a surfactant comprising lecithin in avegetable oil and/or tween 80; and (iv) a therapeutically effectiveamount of insulin conjugated to 1, 2, and/or 3methyl(ethyleneglycol)₇-O-hexanoic acid conjugates in a buffer solution;and (b) having an HLB value between 3 and
 7. 20. The microemulsionformulation of claim 19 wherein the HLB value is from 5 to 6.5.
 21. Themicroemulsion formulation of claim 19 wherein the HLB value is from 5 to6.
 22. The microemulsion formulation of claim 19 wherein the HLB valueis between 5 and
 6. 23. The microemulsion formulation of claim 19wherein the HLB value is 5.0.
 24. The microemulsion formulation of claim19 wherein the HLB value is
 5. 25. The microemulsion formulation ofclaim 19 wherein the aqueous solution is an NaP buffer.
 26. Themicroemulsion formulation of claim 19 further comprising one or morepolyhydroxylic alcohols.
 27. The microemulsion formulation of claim 19with the proviso that the formulation does not comprise a proteaseinhibitor.
 28. A composition for presentation or delivery of aninsulin-methyl(ethyleneglycol)₇-O-hexanoic acid conjugate, saidcomposition: (a) comprising a water-in-oil (w/o) microemulsionincluding: (i) a lipophilic component selected from the group consistingof monoglycerides and diglycerides of medium chain fatty acids; (ii) ahydrophilic component comprising propylene glycol; (iii) a surfactantcomprising lecithin and mannitol; and (iv) a therapeutically effectiveamount of insulin conjugated to 1, 2, and/or 3methyl(ethyleneglycol)₇-O-hexanoic acid conjugates in a buffer solution;and (b) having an HLB value between 3 and
 7. 29. The microemulsionformulation of claim 28 wherein the HLB value is from 5 to 6.5.
 30. Themicroemulsion formulation of claim 28 wherein the HLB value is from 5 to6.
 31. The microemulsion formulation of claim 28 wherein the HLB valueis between 5 and
 6. 32. The microemulsion formulation of claim 28wherein the HLB value is 5.5.
 33. The microemulsion formulation of claim28 wherein the HLB value is 5.49.
 34. The microemulsion formulation ofclaim 28 wherein the aqueous solution is an NaP buffer.
 35. Themicroemulsion formulation of claim 28 further comprising polyethyleneglycol 300 and/or polyethylene glycol
 400. 36. The microemulsionformulation of claim 19 with the proviso that the formulation does notcomprise a protease inhibitor.
 37. A composition for presentation ordelivery of an insulin-methyl(ethyleneglycol)₇-O-hexanoic acidconjugate, said composition: (a) comprising a water-in-oil (w/o)microemulsion including: (i) a lipophilic component selected from thegroup consisting of monoglycerides and diglycerides of medium chainfatty acids; (ii) a hydrophilic component comprising propylene glycol;(iii) two or more surfactants, including lecithin and polyoxyethylenesorbitan monooleate; and (iv) a therapeutically effective amount ofinsulin conjugated to 1, 2, and/or 3 methyl(ethyleneglycol)₇-O-hexanoicacid conjugates in a buffer solution; and (b) having an HLB valuebetween 3 and
 7. 38. The microemulsion formulation of claim 37 whereinthe HLB value is from 5 to 6.5.
 39. The microemulsion formulation ofclaim 37 wherein the HLB value is from 5 to
 6. 40. The microemulsionformulation of claim 37 wherein the HLB value is between 5 and
 6. 41.The microemulsion formulation of claim 37 wherein the HLB value is 5.6.42. The microemulsion formulation of claim 37 wherein the HLB value is5.58.
 43. The microemulsion formulation of claim 37 wherein the aqueoussolution is an NaP buffer.
 44. The microemulsion formulation of claim 37wherein the hydrophilic component comprises polyethylene glycol 300 andpolyethylene glycol
 400. 45. The microemulsion formulation of claim 37with the proviso that the formulation does not comprise a proteaseinhibitor.
 46. A composition for presentation or delivery of aninsulin-methyl(ethyleneglycol)₇-O-hexanoic acid conjugate, saidcomposition: (a) comprising a water-in-oil (w/o) microemulsionincluding: (i) a lipophilic component selected from the group consistingof monoglycerides and diglycerides of medium chain fatty acids; (ii) ahydrophilic component comprising propylene glycol esters; (iii) two ormore surfactants, including lecithin and sodium octanoate; and (iv) atherapeutically effective amount of insulin conjugated to 1, 2, and/or 3methyl(ethyleneglycol)₇-O-hexanoic acid conjugates in a buffer solution;and (b) having an HLB value between 3 and
 7. 47. The microemulsionformulation of claim 46 wherein the HLB value is from 5 to 6.5.
 48. Themicroemulsion formulation of claim 46 wherein the HLB value is from 5 to6.
 49. The microemulsion formulation of claim 46 wherein the HLB valueis between 5 and
 6. 50. The microemulsion formulation of claim 46wherein the HLB value is 5.9.
 51. The microemulsion formulation of claim46 wherein the HLB value is 5.85.
 52. The microemulsion formulation ofclaim 46 wherein the aqueous solution is an NaP buffer.
 53. Themicroemulsion formulation of claim 46 with the proviso that theformulation does not comprise a protease inhibitor.
 54. A compositionfor presentation or delivery of aninsulin-methyl(ethyleneglycol)₇-O-hexanoic acid conjugate, saidcomposition: (a) comprising a water-in-oil (w/o) microemulsionincluding: (i) a lipophilic component selected from the group consistingof monoglycerides and diglycerides of medium chain fatty acids; (ii) ahydrophilic component comprising propylene glycol esters; (iii) asurfactant comprising lecithin; and (iv) a therapeutically effectiveamount o insulin conjugated to 1, 2, and/or 3methyl(ethyleneglycol)₇-O-hexanoic acid coniugates in a buffer solution;and (b) having an HLB value between 3 and
 7. 55. The microemulsionformulation of claim 54 wherein the HLB value is from 5 to 6.5.
 56. Themicroemulsion formulation of claim 54 wherein the HLB value is from 5 to6.
 57. The microemulsion formulation of claim 54 wherein the HLB valueis between 5 and
 6. 58. The microemulsion formulation of claim 54wherein the HLB value is 5.6.
 59. The microemulsion formulation of claim54 wherein the HLB value is 5.58.
 60. The microemulsion formulation ofclaim 54 wherein the aqueous solution is an NaP buffer.
 61. Themicroemulsion formulation of claim 54 with the proviso that theformulation does not comprise a protease inhibitor.